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From first shot to silence of peace: Timeline of World War I

PARIS (AP) — Unleashed by an archduke's assassination, World War I gradually entangled more and more countries, killing millions of soldiers and civilians and touching multiple continents. As the world marks 100 years since the fighting stopped, here is a look at some key moments in WWI:

1914 June 28: Serb teenager Gavrilo Princip kills Austrian Archduke Franz Ferdinand July 28: Austria-Hungary declares war on Serbia Aug. 1: Germany declares war on Russia Aug. 3: Germany declares war on France

Aug. 4: Germany invades Belgium; Britain declares war on Germany Aug. 23: Japan declares war on Germany September: Battle of the Marne stops the German advance in France Oct. 29: Ottoman Empire enters the war

November: Beginning of trench warfare Dec. 25: Unofficial Christmas Truce 1915 February: German U-boat campaign marks first large use of submarines in warfare April: Allied troops land in Gallipoli , Turkey, a defining moment for Australian, New Zealand

April 22: First use of a chemical weapon , chlorine gas, near Ypres, Belgium May 7: British ship Lusitania sunk by German U-boat May 23: Italy enters war, against Austria-Hungary October: Bulgaria joins war, on side of Central Powers

1916 Feb. 21: Battle of Verdun begins March 9: Germany declares war on Portugal July 1: Battle of the Somme begins, with first mass use of tanks Aug. 27: Romania enters war, is invaded by Germany Sept. 4: British take Dar es Salaam in German East Africa

October: Soldier Adolf Hitler wounded Dec. 23: Allied forces defeat Turkish in Sinai Peninsula 1917 March: Baghdad falls to Anglo-Indian forces April 6: United States declares war on Germany April: Battle for Vimy Ridge , defining moment for Canada

July: Last Russian offensive ends in failure, as revolution nears; inconclusive Battle of Passchendaele in Belgium Oct. 15: Spy Mata Hari executed by French firing squad Oct. 26: Brazil declares war, joining Allied Powers

December: Battle of Jerusalem 1918 March 3: Treaty of Brest-Litovsk ends Russia's involvement in the war on the Eastern Front. April 21: Legendary German fighter pilot known as the Red Baron shot down and killed near Amiens, France

June: Battle of Belleau Wood , defining moment for U.S. military July 21: German submarine fires on Cape Cod, only attack on mainland U.S. Sept. 26: Battle of the Meuse-Argonne begins Oct. 30: Ottoman Empire signs armistice with Allies

Oct. 31: Dissolution of Austro-Hungarian Empire Nov. 9: Germany's Kaiser Wilhelm II abdicates Nov. 11: Germany signs armistice ending the war

For more information on World War I, go to The Associated Press' WWI hub:

World War I: An AP Centennial Commemorative Edition. Available now exclusively at Amazon:

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