World War 1 (WWI) was sparked by the assassination of Archduke Franz Ferdinand in 1914 and ended with the Treaty of Versailles in 1919.
- June 28 – Archduke Franz Ferdinand, heir to Austria-Hungary’s throne, and his wife, Sophie, are assassinated by Serbian nationalist Gavrilo Princip while the couple were visiting Sarajevo.
- July 28 – Austria-Hungary declares war on Serbia.
- August 1 – Germany declares war on Russia.
- August 3 – Germany declares war on France.
- August 4 – The United Kingdom declares war on Germany, after Germany invades Belgium.
- August 6 – Austria-Hungary declares war on Russia and Serbia declares war on Germany.
- August 26 – The Battle of Tannenberg begins.
- August 19 – U.S. President Woodrow Wilson announces the U.S. will remain neutral.
- September 5 – The First Battle of the Marne begins. Trench warfare begins as soldiers on both sides dig in.
- October 19 – Battle of Ypres begins.
- November 3 – The United Kingdom announces that the North Sea is a military area, effectively creating a blockade of goods into Germany.
- December 24 The unofficial Christmas truce is declared.
- February 4 – Germany declares a “war zone” around Great Britain, essentially effecting a submarine blockade where even neutral merchant vessels were to be potential targets.
- February 19 – The Dardanelles Campaign begins.
- April 22 – The Second Battle of Ypres begins. It is during this battle that the Germans first use poison gas.
- April 25 – The Battle of Gallipoli begins.
- May 7 – The British ocean liner RMS Lusitania is sunk by German U-boat, U-20
- September 5 – Tsar Nicholas II takes personal control over Russia’s armies.
- February 21 – The Battle of Verdun begins. The Battle of Verdun was the longest battle of World War I and was one of the bloodiest.
- May 31 – The Battle of Jutland, the major naval battle of the war, begins.
- July 1 – The Battle of the Somme begins. During the Battle of the Somme, tanks are first introduced into battle.
- January 19 – Germany sends the secret Zimmerman Telegram to Mexico in an effort to entice Mexico to join the war. The British intercept and decipher the coded message.
- March 15 – Russian Tsar Nicholas II abdicates.
- April 6 – The United States declares war on Germany.
- July 31 – The Battle of Passchendaele (also known as the Third Battle of Ypres) begins.
- November 7 – The Bolsheviks successfully overthrow the Russian government.
- December 17 – The armistice agreed upon between the new Russian government and the Central Powers goes into effect.
- January 8 – U.S. President Woodrow Wilson issues his Fourteen Points to peace.
- March 3 – Russia signs the Treaty of Brest Litovsk, which is a peace treaty between Russia and the Central Powers.
- March 21 – Germany launches the Spring Offensive.
- April 21 – German flying ace, Baron Manfred von Richthofen (more commonly known as the Red Baron), is shot down.
- July 15 – The Second Battle of the Marne begins.
- November 9 – German Kaiser Wilhelm II abdicates and flees Germany.
- November 11 – Germany signs the armistice at Compiegne, France. Fighting ends on the 11th hour of the 11th day of the 11th month.
- June 28 – The Treaty of Versailles officially ends WWI.