1910

• Beginning of the Mexican Revolution.
• George V becomes King of the United Kingdom and the British Dominions and Emperor of India.
• Union of South Africa created.
• 5 October 1910 revolution in Portugal and proclamation of the First Portuguese Republic.

1911

• Xinhai Revolution in China overthrows the Qing Dynasty.
• Roald Amundsen first reaches the South Pole.
• Triangle Shirtwaist Factory fire results in the deaths of 146 workers and leads to sweeping workplace safety reforms.

1912

• End of the Chinese Empire. Republic of China established.
• The African National Congress is founded.
• Morocco becomes a protectorate of France.
• Sinking of the RMS Titanic.
• United States occupation of Nicaragua begins.

1913

• Niels Bohr formulates the first cohesive model of the atomic nucleus, and in the process paves the way to quantum mechanics.

1914

• Gavrilo Princip assassinates Archduke Franz Ferdinand of Austria in Sarajevo, triggering the start of World War I.
• First Battle of the Marne.
• The United Kingdom establishes the Sultanate of Egypt as a protectorate.
• Benedict XV becomes Pope.

1915

• The RMS Lusitania is sunk.
• The United States occupation of Haiti begins.
• Armenian genocide in the Ottoman Empire.
• The Treaty of London brings Italy into the war.

1916

• Easter Rising in Ireland.
• The implementation of daylight saving time.
• Brusilov Offensive.
• Warlord Era begins in China.

1917

• Russian Revolution ends the Russian Empire; beginning of Russian Civil War.
• Battle of Passchendaele.
• USA joins the Allies for the last 17 months of World War I.
• Battle of Caporetto.
• Independence of Poland and Finland recognized.

1918

• Armistice of 11 November 1918 ends World War I.
• German Revolution begins.
• Abdication of Kaiser Wilhelm II.
• Spanish flu pandemic.
• Assassination of Tsar Nicholas II and his family.
• Poland, Ukraine and Belarus are among a number of states to declare independence from Russia.

1919

• Treaty of Versailles redraws European borders.
• German Revolution ends with the collapse of the German Empire and the establishment of the Weimar Republic.
• Victory for Estonia in the Estonian War of Independence.
• League of Nations founded in Paris.
• Polish-Soviet War begins.
• The Italian National Fascist Party is established by Benito Mussolini.

1920

• Mexican Revolution ends.
• Greece restores its monarchy after a referendum.
• Mandatory Palestine established.
• Prohibition in the United States enforced.

1921

• Adolf Hitler becomes Führer of the Nazi Party as hyperinflation in the Weimar Republic begins.
• Russia invades Georgia and incorporates it into the Soviet Union.
• End of Russian Civil War, Polish-Soviet War and Ukrainian–Soviet War.
• Coup brings the Pahlavi dynasty to power in Iran.
• Warren G. Harding becomes 29th President of The United States

1922

• Ottoman Sultanate abolished by the Turkish Grand National Assembly; Sultan Mehmed VI is deposed.
• Irish Free State is established, while the Province of Northern Ireland is created within The United Kingdom.
• The Irish Civil War begins.

1923

• Hyperinflation in the Weimar Republic ends with the introduction of the Rentenmark.
• Time Magazine is first published.

1924

• Death of Vladimir Lenin triggers power struggle between Leon Trotsky and Joseph Stalin.
• The Caliphate is abolished by Kemal Atatürk.

1925

• Benito Mussolini gains dictatorial powers in Italy.
• Mein Kampf is published.
• First televisual image created by John Logie Baird.
• Locarno Treaties are signed.
• Serum run to Nome.

1926

• Hirohito becomes Emperor of Japan.
• Coups in Greece, Poland and Portugal install new dictatorships.

1927

• The Jazz Singer, the first "talkie", is released.
• Joseph Stalin becomes leader of the Soviet Union.
• Chinese Civil War begins.
• Bath School disaster.
• World population reaches 2 billion.

1928

• Discovery of penicillin by Alexander Fleming.
• Warlord Era ends in China.
• Malta becomes a British Dominion.
• Bubble gum is invented.

1929

• Wall Street crash of 1929 and the beginning of the Great Depression.
• Leon Trotsky is exiled.
• First people sent to the gulag in the Soviet Union as Stalin assumes effective control.

1930

• Vargas Era begins in Brazil
• Aided by the Great Depression, the Nazi Party increases its share of the vote from 2.6% to 18.3%.
• Clyde Tombaugh discovers Pluto.
• First FIFA World Cup hosted.