January
January 1, 1915 — The war enters its second year, with millions mobilized across Europe as trench warfare hardens along the Western Front.
January 19, 1915 — Germany conducts its first Zeppelin bombing raid on Britain.
January 9, 1916 — The Gallipoli Campaign ends with Allied evacuation.
January 31, 1917 — Germany announces unrestricted submarine warfare, increasing tensions with the United States.
January 8, 1918 — President Woodrow Wilson announces his Fourteen Points peace proposal.
January 18, 1919 — The Paris Peace Conference opens, shaping the postwar world and laying groundwork for future global conflict.
February
February 17, 1915 — Germany declares war zone around Britain, escalating naval conflict.
Feb 1, 1916 — Zeppelin raids continue over Britain, bringing war to civilians.
February 21, 1916 — The Battle of Verdun begins, one of the longest and bloodiest battles in modern history.
February 3, 1917 — The U.S. severs diplomatic relations with Germany.
March
March 18, 1915 — Major naval assault on the Dardanelles fails.
March 25, 1915 — Allied naval forces begin major operations against the Ottoman Empire in the Dardanelles.
March 15, 1917 — Tsar Nicholas II abdicates, ending centuries of Russian imperial rule.
March 3, 1918 — Russia signs the Treaty of Brest-Litovsk, exiting the war and reshaping the Eastern Front.
March 21, 1918 — Germany launches the Spring Offensive, its final major push on the Western Front.
April
April 22, 1915 — Poison gas is used on a large scale for the first time at the Second Battle of Ypres.
April 25, 1915 — Allied landings begin at Gallipoli.
April 6, 1917 — The United States declares war on Germany, entering World War I.
April 16, 1917 — French forces begin the disastrous Nivelle Offensive.
April 9, 1917 — Canadian forces capture Vimy Ridge, a defining national moment.
May
May 7, 1915 — The British liner Lusitania is sunk by a German submarine, killing 1,198 people.
May 9, 1915 — Britain launches a costly offensive at Aubers Ridge.
May 15, 1915 — Italy enters the war on the side of the Allies.
May 31, 1916 — The Battle of Jutland, the largest naval battle of the war, takes place in the North Sea.
May 27, 1918 — Germany launches the Third Battle of the Aisne.
June
June 28, 1914 — Archduke Franz Ferdinand is assassinated in Sarajevo, igniting the crisis that led to war.
June 4, 1917 — The U.S. Selective Service Act goes into effect, expanding military mobilization.
June 7, 1917 — The Battle of Messines begins with massive underground explosions.
June 15, 1918 — The Second Battle of the Piave River begins in Italy.
July
July 28, 1914 — Austria-Hungary declares war on Serbia, marking the official start of World War I.
July 1, 1916 — The Battle of the Somme begins, resulting in catastrophic casualties on its first day.
July 31, 1917 — The Third Battle of Ypres (Passchendaele) begins.
July 15, 1918 — The Second Battle of the Marne begins, turning the tide against Germany.
August
August 4, 1914 — Britain declares war on Germany following the invasion of Belgium.
August 21, 1914 — The Battle of Charleroi begins on the Western Front.
August 25, 1914 — The Battle of Tannenberg devastates Russian forces on the Eastern Front.
Aug 8, 1918 — The Battle of Amiens begins, later called the “Black Day” of the German Army.
September
September 5, 1914 — The First Battle of the Marne halts Germany’s advance toward Paris.
September 15, 1916 — Tanks are used in combat for the first time at the Somme.
September 26, 1918 — The Meuse-Argonne Offensive begins, the largest U.S. military operation of the war.
September 29, 1918 — Bulgaria signs an armistice, weakening the Central Powers.
October
October 12, 1917 — Allied forces capture Passchendaele after months of brutal fighting.
October 1, 1918 — Germany requests an armistice as defeat becomes inevitable.
October 30, 1918 — The Ottoman Empire signs the Armistice of Mudros.
November
November 7, 1917 — The Bolshevik Revolution reshapes Russia and the war’s political future.
November 3, 1918 — Austria-Hungary signs an armistice, signaling imperial collapse.
November 9, 1918 — Kaiser Wilhelm II abdicates the German throne.
November 11, 1918 — The Armistice ends fighting on the Western Front.
December
December 25, 1914 — The Christmas Truce sees soldiers briefly cease fire along parts of the Western Front.
December 9, 1917 — British forces capture Jerusalem from the Ottoman Empire.
December 14, 1918 — President Wilson arrives in Europe to negotiate peace.
December 31, 1918 — The world reflects on a war that reshaped nations, lives, and memory forever.