Victoria was Queen of the United Kingdom of Great Britain and Ireland from 20 June 1837 until her death. On 1 May 1876, she adopted the additional title of Empress of India.

Victoria inherited the throne at the age of 18, after her father's three elder brothers had all died leaving no surviving legitimate children. She became a national icon who was identified with strict standards of personal morality. Victoria married her first cousin Prince Albert. After his death in 1861, Victoria plunged into deep mourning and avoided public appearances. As a result, republicanism temporarily gained strength but in the latter half of her reign, her popularity recovered. Her Golden and Diamond Jubilees were times of public celebration.

William Ewart Gladstone (29 December 1809 – 19 May 1898) was a British statesman and Liberal Party politician. In a career lasting over sixty years, he served for twelve years as Prime Minister of the United Kingdom, spread over four terms beginning in 1868 and ending in 1894.

Many reforms were passed during his first ministry, including the disestablishment of the Church of Ireland and the introduction of secret voting. After electoral defeat in 1874, Gladstone resigned as leader of the Liberal Party.

Benjamin Disraeli, 1st Earl of Beaconsfield, (21 December 1804 – 19 April 1881) was a British statesman who twice served as Prime Minister of the United Kingdom.

Disraeli's new government enacted many reforms, including: - the Artisans' and Labourers' Dwellings Improvement Act 1875, which made inexpensive loans available to towns and cities to construct working-class housing. - the Public Health Act 1875, modernising sanitary codes through the nation, - the Sale of Food and Drugs Act (1875) - the Education Act (1876). - the Factory Act meant to protect workers, - the Conspiracy, and Protection of Property Act 1875, which allowed peaceful picketing - the Employers and Workmen Act (1875) to enable workers to sue employers in the civil courts if they broke legal contracts.

As a result of these social reforms the Liberal-Labour MP Alexander Macdonald said, "The Conservative party have done more for the working classes in five years than the Liberals have in fifty."

"Mr. Watson — Come here — I want to see you" were the first intelligible words spoken over the telephone, as recorded in Bell's Journal entry (10 March 1876). These are often misquoted as "Mr. Watson, come here, I want you." Watson later recounted that Bell had spilled battery acid and had called for him over the phone with these words, but this may have been in a separate incident.

Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). His work is also known for its influence on the philosophy of science.

He is best known to the general public for his mass–energy equivalence formula E = mc2, which has been dubbed "the world's most famous equation". He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect", a pivotal step in the development of quantum theory.

William Ewart Gladstone (29 December 1809 – 19 May 1898) was a British statesman and Liberal Party politician. In a career lasting over sixty years, he served for twelve years as Prime Minister of the United Kingdom, spread over four terms beginning in 1868 and ending in 1894.

Historians have debated the wisdom of Gladstone's foreign-policy during his second ministry. Paul Hayes says it "provides one of the most intriguing and perplexing tales of muddle and incompetence in foreign affairs, unsurpassed in modern political history until the days of Grey and, later, Neville Chamberlain."

Sir Alexander Fleming (6 August 1881 – 11 March 1955) was a Scottish physician, microbiologist, and pharmacologist. His best-known discoveries are the enzyme lysozyme in 1923 and the world's first antibiotic substance benzylpenicillin (Penicillin G) from the mould Penicillium notatum in 1928, for which he shared the Nobel Prize in Physiology or Medicine in 1945 with Howard Florey and Ernst Boris Chain. He wrote many articles on bacteriology, immunology, and chemotherapy.

A prime meridian, based at the Royal Observatory, Greenwich, in London was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of US President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., United States, for the International Meridian Conference. This conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. However, France abstained from the vote, and French maps continued to use the Paris meridian for several decades.

Robert Arthur Talbot Gascoyne-Cecil, 3rd Marquess of Salisbury, (3 February 1830 – 22 August 1903), styled Lord Robert Cecil before 1865 and Viscount Cranborne from June 1865 until April 1868, was a British statesman and Conservative Party politician, serving as Prime Minister three times for a total of over thirteen years. He was the last Prime Minister to head his full administration from the House of Lords.

He became Prime Minister of a minority administration from 1885 to 1886. In the November 1883 issue of National Review Salisbury wrote an article titled "Labourers' and Artisans' Dwellings" in which he argued that the poor conditions of working class housing were injurious to morality and health

William Ewart Gladstone (29 December 1809 – 19 May 1898) was a British statesman and Liberal Party politician. In a career lasting over sixty years, he served for twelve years as Prime Minister of the United Kingdom, spread over four terms beginning in 1868 and ending in 1894.

During this administration he first introduced his Home Rule Bill for Ireland. The issue split the Liberal Party (a breakaway group went on to create the Liberal Unionist party) and the bill was thrown out on the second reading, ending his government after only a few months and inaugurating another headed by Lord Salisbury.

Robert Arthur Talbot Gascoyne-Cecil, 3rd Marquess of Salisbury, (3 February 1830 – 22 August 1903), styled Lord Robert Cecil before 1865 and Viscount Cranborne from June 1865 until April 1868, was a British statesman and Conservative Party politician, serving as Prime Minister three times for a total of over thirteen years. He was the last Prime Minister to head his full administration from the House of Lords.

In 1889 Salisbury set up the London County Council and then in 1890 allowed it to build houses. However, he came to regret this, saying in November 1894 that the LCC, "is the place where collectivist and socialistic experiments are tried. It is the place where a new revolutionary spirit finds its instruments and collects its arms".

John Logie Baird (13 August 1888 – 14 June 1946) was a Scottish engineer, innovator, one of the inventors of the mechanical television, demonstrating the first working television system on 26 January 1926, and inventor of both the first publicly demonstrated colour television system, and the first purely electronic colour television picture tube.

In 1928 the Baird Television Development Company achieved the first transatlantic television transmission. Baird's early technological successes and his role in the practical introduction of broadcast television for home entertainment have earned him a prominent place in television's history.

Sir James Chadwick was an English physicist. When his university Professor, Ernest Rutherford became the Director of Research at Cavendish Lab, he invited Chadwick to join him. While there, he discovered the neutron, for which he won the 1935 Nobel Prize in Physics. It led to the development of the atomic bomb. He was distressed that his discovery had been used to kill many innocent people

Ellis Island, in Upper New York Bay, was the gateway for over 12 million immigrants to the U.S. as the United States' busiest immigrant inspection station for over 60 years from 1892 until 1954. Ellis Island was opened January 1, 1892. The island was greatly expanded with land reclamation between 1892 and 1934. Before that, the much smaller original island was the site of Fort Gibson and later a naval magazine.

The island was made part of the Statue of Liberty National Monument in 1965 and has hosted a museum of immigration since 1990. "As a visitor to this place, you stand in awe. It has the aura of an ancient cathedral, redolent with the millions who passed through these doors."

William Ewart Gladstone (29 December 1809 – 19 May 1898) was a British statesman and Liberal Party politician. In a career lasting over sixty years, he served for twelve years as Prime Minister of the United Kingdom, spread over four terms beginning in 1868 and ending in 1894.

The general election of 1892 resulted in a minority Liberal government with Gladstone as Prime Minister. The electoral address had promised Irish Home Rule and the disestablishment of the Scottish and Welsh Churches.[118] In February 1893 he introduced the Second Home Rule Bill, which was passed in the Commons at second reading on 21 April by 43 votes and third reading on 1 September by 34 votes. The House of Lords defeated the bill by voting against by 419 votes to 41 on 8 September.

London’s iconic Tower Bridge opens. The bridge’s twin towers, high-level walkways and Victorian engine rooms now form part of the Tower Bridge Exhibition.

Tower Bridge was built to ease road traffic while maintaining river access to the busy Pool of London docks. Built with giant moveable roadways that lift up for passing ships, it is to this day considered an engineering marvel and beyond being one of London’s favourite icons, it is arguably one of the most famous and instantly recognisable structures in the entire world.

Archibald Philip Primrose, 5th Earl of Rosebery, 1st Earl of Midlothian, (7 May 1847 – 21 May 1929) was a British Liberal politician who served as Prime Minister of the United Kingdom from March 1894 to June 1895.

Rosebery's government was largely unsuccessful, as in the Armenian crisis of 1895–96. He spoke out for a strongly pro-Armenian and anti-Turkish policy. Gladstone, a prime minister in retirement, called on Britain to intervene alone. The added pressure weakened Rosebery.His designs in foreign policy, such as expansion of the fleet, were defeated by disagreements within the Liberal Party. He angered all the European powers.

Robert Arthur Talbot Gascoyne-Cecil, 3rd Marquess of Salisbury, (3 February 1830 – 22 August 1903), styled Lord Robert Cecil before 1865 and Viscount Cranborne from June 1865 until April 1868, was a British statesman and Conservative Party politician, serving as Prime Minister three times for a total of over thirteen years. He was the last Prime Minister to head his full administration from the House of Lords.

Among the important events of his premierships was the Scramble for Africa, culminating in the Fashoda Incident which escalated tensions with France, and the long, brutal and unpopular Second Boer War in South Africa.

Sir John Douglas Cockcroft was a British physicist who shared the 1951 Nobel Prize in Physics with Ernest Walton for their work on splitting the atom. His university studies were cut short by WWI. Afterwards he resumed his studies and on graduating he worked with Rutherford in the Cavendish Labs. He collaborated with Ernest Walton and their research was instrumental in the development of nuclear power.

The Spanish–American War was fought between the United States and Spain in 1898. Hostilities began in the aftermath of the internal explosion of USS Maine in Havana Harbor in Cuba, leading to U.S. intervention in the Cuban War of Independence. U.S. acquisition of Spain's Pacific possessions led to its involvement in the Philippine Revolution and ultimately in the Philippine–American War.

The result was the 1898 Treaty of Paris, negotiated on terms favorable to the U.S. which allowed it temporary control of Cuba and ceded ownership of Puerto Rico, Guam, and the Philippine islands. The cession of the Philippines involved payment of $20 million ($602,320,000 today) to Spain by the U.S. to cover infrastructure owned by Spain.

The Philippine–American War, was an armed conflict between the First Philippine Republic and the United States that lasted from February 4, 1899, to July 2, 1902. While Filipino nationalists viewed the conflict as a continuation of the struggle for independence that began in 1896 with the Philippine Revolution, the U.S. government regarded it as an insurrection. The conflict arose when the First Philippine Republic objected to the terms of the Treaty of Paris under which the United States took possession of the Philippines from Spain, ending the short Spanish–American War.

The war, and especially the following occupation by the U.S., changed the culture of the islands, leading to the disestablishment of the Catholic Church in the Philippines as a state religion, and the introduction of English to the islands as the primary language of government, education, business, industry, and, in future decades, among upper-class families and educated individuals.

The Boxer Rebellion was an anti-foreign, anti-colonial, and anti-Christian uprising that took place in China between 1899 and 1901, toward the end of the Qing dynasty. They were motivated by proto-nationalist sentiments and by opposition to Western colonialism and the Christian missionary activity that was associated with it.

The Boxer Protocol of 7 September 1901 provided for the execution of government officials who had supported the Boxers, provisions for foreign troops to be stationed in Beijing, and 450 million taels of silver—approximately $10 billion at 2018 silver prices and more than the government's annual tax revenue—to be paid as indemnity over the course of the next thirty-nine years to the eight nations involved. The Empress Dowager then sponsored a set of institutional and fiscal changes in a failed attempt to save the dynasty.

Fought by Britain and her Empire against the descendants of the Dutch settlers (Boers) in the Transvaal region of South Africa, the Second Boer War highlighted the limitations of 19th C military methods, employing for the first time modern automatic weapons and high explosives to decimate the enemy

Edward VII was King of the United Kingdom of Great Britain and Ireland and Emperor of India from 22 January 1901 until his death in 1910. The eldest son of Queen Victoria and Prince Albert, Edward was related to royalty throughout Europe. During his mother's long reign he was excluded from political power, and personified the fashionable, leisured elite. Despite public approval his reputation as a playboy prince soured his relationship with his mother.

As king, Edward fostered good relations between Britain and other European countries, especially France, for which he was popularly called "Peacemaker", but his relationship with his nephew, the German Emperor Wilhelm II, was poor. The Edwardian era, which covered Edward's reign and was named after him, coincided with the start of a new century and heralded significant changes in technology and society, including steam turbine propulsion and the rise of socialism

Arthur James Balfour, 1st Earl of Balfour, (25 July 1848 – 19 March 1930) was a British statesman and Conservative Party politician who served as Prime Minister of the United Kingdom from 1902 to 1905.

He oversaw reform of British defence policy and secured the Entente Cordiale with France, leaving Germany in the cold. Resignations from the Cabinet over tariffs left his party divided. He also suffered from public anger at the later stages of the Boer war and the importation of Chinese labour to South Africa.

Paul Dirac was an English theoretical physicist and one of the pioneers in quantum mechanics and quantum electrodynamics. He proposed the existence of anti-matter purely on the basis of his mathematical logic. The winner of several prestigious awards including the 1933 Nobel Prize for physics which he shared with Erwin Schrödinger, he turned down a knighthood as he did not want to be addressed by his first name.

Sir Henry Campbell-Bannerman (7 September 1836 – 22 April 1908) was a British statesman and Liberal Party politician who served as Prime Minister of the United Kingdom from 1905 to 1908. He was the first First Lord of the Treasury to be officially called "Prime Minister", the term only coming into official usage five days after he took office.

When Arthur Balfour resigned as Prime Minister, Edward VII invited Campbell-Bannerman to form a minority government as the first Liberal Prime Minister of the 20th century. At 69, he was the oldest person to become Prime Minister for the first time in the 20th century. He almost immediately dissolved Parliament and called a general election.

Air Commodore Sir Frank Whittle, (1 June 1907 – 9 August 1996) was a British Royal Air Force air officer. He is credited with single-handedly inventing the turbojet engine. A patent was submitted by Maxime Guillaume in 1921 for a similar invention; however, this was technically unfeasible at the time. Whittle's jet engines were developed some years earlier than those of Germany's Hans von Ohain who was the designer of the first operational turbojet engine.

Herbert Henry Asquith, 1st Earl of Oxford and Asquith, (12 September 1852 – 15 February 1928), generally known as H. H. Asquith, was a British statesman and Liberal Party politician who served as Prime Minister of the United Kingdom from 1908 to 1916.

He was the last prime minister to lead a majority Liberal government. He played a central role in the design and passage of major liberal legislation and a reduction of the power of the House of Lords. In August 1914, Asquith took Great Britain and the British Empire into the First World War. In 1915 his government was vigorously attacked for the shortage of munitions and the failure at Gallipoli. He formed a coalition government with the other parties but failed to satisfy critics. He was forced to resign in December 1916 and never regained power.

George V's reign saw the rise of socialism, communism, fascism, Irish republicanism, and the Indian independence movement, all of which radically changed the political landscape. The Parliament Act 1911 established the supremacy of the elected British House of Commons over the unelected House of Lords. As a result of the First World War (1914–1918), the empires of his first cousins Tsar Nicholas II of Russia and Kaiser Wilhelm II of Germany fell, while the British Empire expanded to its greatest effective extent.

In 1917, George became the first monarch of the House of Windsor, which he renamed from the House of Saxe-Coburg and Gotha as a result of anti-German public sentiment. In 1924 he appointed the first Labour ministry and in 1931 the Statute of Westminster recognised the dominions of the Empire as separate, independent states within the Commonwealth of Nations.

RMS Titanic sank in the early morning of 15 Apr 1912, 4 days into its maiden voyage from Southampton to New York. The largest liner in service at the time, her sinking killed over 1,500 people, one of the deadliest peacetime maritime disasters in history. The disaster caused widespread outrage over the lack of lifeboats, lax regulations, and unequal treatment of the 3 passenger classes during evacuation

Computers owe their existence to British mathematician, Alan Turing. A child prodigy, he went on to pursue his PhD at Princeton University. He was an important member of a group of code-breakers in the Government Code and Cypher School in Bletchley Park and was given the daunting task of deciphering the ever-changing German codes sent by Enigma. He and his team of code-breakers were successful. Despite his part in ensuring the defeat of Germany he was prosecuted for his homosexuality, and committed suicide. In 2009 the British government issued a public apology for the way he was treated and in 2013 he was posthumously pardoned.

World War I (often abbreviated as WWI or WW1), also known as the First World War or the Great War, was a global war originating in Europe. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history. It was also one of the deadliest conflicts in history; an estimated nine million combatants and seven million civilians died as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide.

The Sinking of RMS Lusitania occurred on Friday, 7 May 1915 during WWI, as Germany waged submarine warfare against the UK which had implemented a naval blockade of Germany. The ship was torpedoed by a U-boat and sank in 18 minutes, killing 1,198 and leaving 761 survivors. The sinking turned public opinion in many countries against Germany, and contributed to the American entry into WWI

Born in New Zealand, Maurice Wilkins was a biophysicist awarded the Nobel Prize in Physiology or Medicine. He worked in the Manhattan project but lost interest in nuclear weapons and changed to biophysics. He and Rosalind Franklin provided the secondary research to the double helix theory. He shared the Nobel Prize with Watson and Crick as Franklin died in 1958.

The Easter Rising was an armed insurrection in Ireland during Easter, launched by Irish republicans to end British rule in Ireland. 485 people were killed, over 2,600 wounded. Many of the civilians were killed as a result of the British using artillery and heavy machine guns, or mistaking civilians for rebels. Others were caught in the crossfire in a crowded city. It left parts of Dublin in ruins

Francis Crick was an English molecular biologist, biophysicist, and neuroscientist. He is the co-discoverer of the structure of the DNA molecule. He, along with Watson and Maurice Wilkins were jointly awarded the 1962 Nobel Prize for Physiology or Medicine ‘for their discoveries concerning the molecular structure of nucleic acids, the Double Helix and its significance for information transfer in living material’

David Lloyd George, 1st Earl Lloyd-George of Dwyfor, (17 January 1863 – 26 March 1945) was a British statesman and Liberal Party politician. He was the final Liberal to serve as Prime Minister of the United Kingdom.

As Chancellor of the Exchequer (1908–1915) during H. H. Asquith's tenure as Prime Minister, Lloyd George was a key figure in the introduction of many reforms which laid the foundations of the modern welfare state. His most important role came as the highly energetic Prime Minister of the Wartime Coalition Government (1916–22), during and immediately after the First World War. He was a major player at the Paris Peace Conference of 1919 that reordered Europe after the defeat of the Central Powers.

The Zimmermann Telegram (or Zimmermann Note or Zimmerman Cable) was a secret diplomatic communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico. In the event that the United States entered World War I against Germany, Mexico would recover Texas, Arizona and New Mexico. The telegram was intercepted and decoded by British intelligence. Revelation of the contents enraged Americans, especially after German Foreign Secretary Arthur Zimmermann publicly admitted the telegram was genuine on March 3, and helped generate support for the United States declaration of war on Germany in April. The decryption was described as the most significant intelligence triumph for Britain during World War I, and one of the earliest occasions on which a piece of signal intelligence influenced world events.

As WWI moved to its end the world was swept with a pandemic of epic proportions, killing more people than the fighting. It was called Spanish Flu because it only became widely reported when it reached neutral Spain, press censorship having suppressed news of it elsewhere. One theory is that it was brought to Europe by US Troops. patient zero having been traced to a military training camp in the United States

Rosalind Franklin was a renowned English chemist who did pioneering work in X-ray crystallography. Her most important discovery was the structure of DNA molecule. Working with Maurice Wilkins and a doctorate student Raymond Gosling, she was able to correctly assess the structure of DNA. Her theory that DNA consists of two helical structures was later confirmed by scientists James Watson and Francis Crick

Andrew Bonar Law (16 September 1858 – 30 October 1923), commonly called Bonar Law was a British Conservative politician who served as Prime Minister of the United Kingdom from 1922 to 1923

Bonar Law was the shortest-serving PM of the 20th century. He is often referred to as "the unknown Prime Minister", not least because of a biography of that title by Robert Blake; the name comes from a remark by Asquith at Bonar Law's funeral, that they were burying the Unknown Prime Minister next to the Tomb of the Unknown Soldier. Sir Steven Runciman is reported to have said that he had known all British Prime Ministers in his lifetime, except Bonar Law whom no one knew.

Stanley Baldwin, 1st Earl Baldwin of Bewdley, (3 August 1867 – 14 December 1947) was a British statesman and Conservative Party politician who dominated the government in his country between the world wars. Three times Prime Minister, he is the only British prime minister to have served under three monarchs.

Upon Bonar Law's resignation due to health reasons in May 1923, Baldwin became Prime Minister and Leader of the Conservative Party. He called an election on the issue of tariffs and lost the Conservatives' parliamentary majority, after which Ramsay MacDonald formed a minority Labour government.

James Ramsay MacDonald FRS (12 October 1866 – 9 November 1937) was a British statesman who served as Prime Minister of the United Kingdom from 1929 to 1935. He was the first Labour Party politician to become Prime Minister, leading minority Labour governments in 1924 and in 1929–31. He headed a National Government from 1931 to 1935, dominated by the Conservative Party and supported by only a few Labour members.

In 1924, his first priority was to undo the perceived damage caused by the 1919 Treaty of Versailles, by settling the reparations issue and coming to terms with Germany. The king noted in his diary, "He wishes to do the right thing.... Today 23 years ago dear Grandmama died. I wonder what she would have thought of a Labour Government!"

Stanley Baldwin, 1st Earl Baldwin of Bewdley, (3 August 1867 – 14 December 1947) was a British statesman and Conservative Party politician who dominated the government in his country between the world wars. Three times Prime Minister, he is the only British prime minister to have served under three monarchs.

Baldwin's second government saw reforms in areas formerly associated with the Liberal Party. They included industrial conciliation, unemployment insurance, a more extensive old-age pension system, slum clearance, more private housing, and expansion of maternal and childcare. His government also saw the General Strike in 1926 and the Trade Disputes and Trade Unions Act 1927 to curb the powers of trade unions.

John Logie Baird makes the first public demonstration of a mechanical television on 26 January at Selfridge's department store in London (the first successful transmissions were in early 1923 and February 1924). Later, in July 1928, he demonstrated the first colour television.

The Representation of the People (Equal Franchise) Act 1928 was an Act of the Parliament of the United Kingdom. This act expanded on the Representation of the People Act 1918 which had given some women the vote in Parliamentary elections for the first time after World War I. The 1928 Act widened suffrage by giving women electoral equality with men. It gave the vote to all women over 21 years old, regardless of property ownership. Prior to this act only women over 30 who met minimum property qualifications could vote.

James Watson is an American molecular biologist, geneticist and zoologist who co-discovered the molecular structure of DNA. His discovery has been described by other biologists and Nobel laureates as the most important scientific discovery of the 20th C. Crick, Wilkins and Watson discovered the double helix structure of the DNA molecule

The effects of penicillium mould were isolated in 1928 by Scottish scientist Alexander Fleming, in his laboratory in the basement of St Mary's Hospital in London (now part of Imperial College). Fleming coined the term "penicillin"

MartinLuther King Jr was a leader of the African-American Civil Rights Movement. While fighting injustice meted out to African-Americans, he shunned violence. He used Christian doctrines but he looked towards Mahatma Gandhi’s non-violent movement. He dreamt that one day every human being would be judged by their ability, not skin colour. He died from a white fanatic’s bullet aged 39

James Ramsay MacDonald FRS (12 October 1866 – 9 November 1937) was a British statesman who served as Prime Minister of the United Kingdom from 1929 to 1935. He was the first Labour Party politician to become Prime Minister, leading minority Labour governments in 1924 and in 1929–31. He headed a National Government from 1931 to 1935, dominated by the Conservative Party and supported by only a few Labour members.

MacDonald's second government was in a stronger parliamentary position than his first, and in 1930 he was able to raise unemployment pay, pass an act to improve wages and conditions in the coal industry (i.e. the issues behind the General Strike) and pass a housing act which focused on slum clearances. In 1931, in the aftermath of the Great Depression, he was forced to form a National Government with the Conservatives and Liberals.

The Great Depression was a severe worldwide economic depression that took place mostly during the 1930s, beginning in the United States. The timing of the Great Depression varied across nations; in most countries it started in 1929 and lasted until the late-1930s. It was the longest, deepest, and most widespread depression of the 20th century.

The Great Depression started in the United States after a major fall in stock prices that began around September 4, 1929, and became worldwide news with the stock market crash of October 29, 1929 (known as Black Tuesday). Between 1929 and 1932, worldwide gross domestic product (GDP) fell by an estimated 15%. By comparison, worldwide GDP fell by less than 1% from 2008 to 2009 during the Great Recession. Some economies started to recover by the mid-1930s. However, in many countries the negative effects of the Great Depression lasted until the beginning of World War II.