Archduke Franz Ferdinand of Austria and his wife, Sophie, are assassinated by a Bosnian Serb nationalist in Sarajevo.
World War I Begins
July 28, 1914
Austria-Hungary declares war on Serbia, marking the beginning of World War I.
Declarations of War
August 1–28, 1914
Multiple countries declare war on each other, including Germany on Russia, France, and Belgium; Britain on Germany; Austria on Russia; Montenegro on Austria; France on Austria; Britain on Austria; Montenegro on Germany; Japan on Germany; and Austria on Belgium.
First Battle of the Marne
September 6, 1914
The First Battle of the Marne begins, halting the German advance and preventing the capture of Paris.
Britain and France Declare War on the Ottoman Empire
November 5, 1914
Britain and France declare war on the Ottoman Empire, bringing the empire into the conflict.
Second Battle of Ypres
April 22, 1915
The Second Battle of Ypres begins, marking the first large-scale use of poison gas on the Western Front.
Gallipoli Campaign
April 25, 1915
Landings begin on the Gallipoli Peninsula at Cape Helles, marking the start of a disastrous Allied campaign to seize the Dardanelles Strait.
Sinking of the Lusitania
May 7, 1915
The British ocean liner Lusitania is torpedoed by a German U-boat off the southern coast of Ireland, killing 1,198 people, including 128 Americans.
Battle of Verdun
February 21 - December 18, 1916
The Battle of Verdun, one of the longest and deadliest battles of the war, takes place with heavy casualties on both sides.
Battle of Jutland
May 31, 1916
The British and German fleets meet 60 miles off the coast of Jutland, Denmark, in the war’s only major encounter between the world’s two largest sea powers.
Battle of the Somme
July 1 - November 18, 1916
The Battle of the Somme, one of the bloodiest battles of the war, takes place with over a million casualties.
Tsar Nicholas II Abdicates
March 15, 1917
Tsar Nicholas II abdicates the throne after a week of riots in the Russian capital of St. Petersburg.
U.S. Declares War on Germany
April 6, 1917
The United States declares war on Germany, entering the conflict on the side of the Allies.
Battle of Arras and Vimy Ridge
April 9-12, 1917
Canadian Corps launch a successful attack against German defenses using miles of tunnels and aerial reconnaissance. The battle results in 10,602 Canadian casualties and 20,000 German casualties.
Second Battle of the Aisne
April 16-May 9, 1917
The disastrous centerpiece of the French armies' Nivelle offensive, leading to widespread mutiny. Total French losses are 187,000, while German losses are estimated at 168,000.
Battle of Messines
June 7-14, 1917
Detonation of 19 mines beneath German positions enables Allied infantry to capture the salient. This battle is the first on the Western Front to see defensive casualties exceed attacking losses: 25,000 against 17,000.
Third Battle of Ypres (Passchendaele)
July 31-November 6, 1917
Intended to be the major breakthrough in Flanders, Allied progress is slowed by terrible mud. The British Expeditionary Force suffers approximately 310,000 casualties, while the Germans suffer 260,000 casualties.
First Use of Tanks in Combat
November 20, 1917
A British offensive at Cambrai, France, marks the first large-scale use of tanks in combat.
Treaty of Brest-Litovsk
March 3, 1918
The Soviet government concludes a separate peace with the Central Powers, accepting the Treaty of Brest-Litovsk. Russia surrenders its claim to Ukraine, its Polish and Baltic territories, and Finland.
Third Battle of the Aisne
May 27-June 6, 1918
Intended to ensure all-out German victory before US intervention, initial gains are halted by poor supplies and reserve support. France loses 98,000, Britain 29,000, and German losses are similar.
Battle of Cantigny
May 28, 1918
In its first major offensive, the American army captures the village of Cantigny from the German Eighteenth Army. US forces suffer 1,067 casualties and capture around 100 German prisoners.
Battles of Chateau Thierry and Belleau Wood
June 3-26, 1918
US troops recapture German-held positions. US forces lose 9,777, and some 1,600 Germans are taken prisoner.
Second Battle of the Marne
July 15-August 5, 1918
Initially conceived to divert Allied forces away from Flanders, the German attack falters, allowing a decisive counter-attack. France loses 95,000, Britain 13,000, the US 12,000, and Germany 168,000.
Armistice Day
November 11, 1918
Germany and the Allies conclude an armistice based largely on US President Woodrow Wilson's Fourteen Points, marking the end of World War I.