June 28 - Archduke Franz Ferdinand, prince to the Austria-Hungary throne, is assassinated in Sarajevo by a Serbian named Gavrilo Princip.
July 23 - Austria-Hungary makes demands on Serbia for retribution. Serbia does not meet demands.
July 28 - Austria-Hungary declares war on Serbia. Russia begins mobilizing its troops.
August 1 - Germany declares war on Russia.
August 3 - Germany declares war on France as part of the Schlieffen Plan.
August 4 - Germany invades Belgium. Britain declares war on Germany.
August 23 to 30 - The Battle of Tannenberg is fought between Germany and Russia. The Germans defeat the Russian Second Army.
September 5 to 12 - The advancing German army is stopped before Paris by the British and French at the First Battle of the Marne. The Germans dig in and four years of trench warfare begins.
October 19 to November 22 - The Allies defeat the Germans at the First Battle of Ypres.
November 2 - The British begin a naval blockade of Germany.
November 11 - The Ottoman Empire declares war on the Allies.
December 24 - An unofficial truce is declared between the two sides at Christmas.
1915
February 4 - The Germans begin to use submarines against Allied merchant ships around the island of Britain.
April 25 - The Allies attack the Ottoman Empire at the Battle of Gallipoli. This campaign will last over eight months and will end as a victory for the Ottomans and the retreat of the Allies.
May 7 - The Lusitania, a luxury British passenger ship, is sunk by a German submarine. 1,195 civilians were killed. This act sparks international outrage and contributes to the United States joining the war against Germany.
October 14 - Bulgaria enters the war by declaring war on Serbia.
1916
February 21 - The Battle of Verdun begins between France and Germany. This battle will last until December of 1916 and will finally result in a French victory.
May 31 - The largest naval battle of the war, the Battle of Jutland, is fought between Britain and Germany in the North Sea.
July 1 - The Battle of the Somme begins. Over 1 million soldiers will be wounded or killed.
1917
January 19 - The British intercept the Zimmerman Telegram in which Germany tries to convince Mexico to join the war. This will result in the United States declaring war on Germany.
March 8 - The Russian Revolution begins. Tsar Nicholas II is removed from power on March 15.
April 6 - The United States enters the war, declaring war on Germany.
November 7 - The Bolsheviks, led by Vladimir Lenin, overthrow the Russian government.
December 17 - The Russians agree to peace with the Central powers and leave the war.
1918
January 8 - President Woodrow Wilson issues his "Fourteen Points" for peace and an end to the war.
March 21 - Germany launches the Spring Offensive hoping to defeat the Allies before reinforcements from the United States can be deployed.
July 15 - The Second Battle of the Marne begins. This battle will end on August 6 as a decisive victory for the Allies.
November 11 - Germany agrees to an armistice and the fighting comes to an end at 11am on the 11th day of the 11th month.
1919
June 28 - The Treaty of Versailles is signed by Germany and World War I comes to an end.
