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Archduke Franz Ferdinand, heir to the throne of the Austro-Hungarian Empire, and his wife are assassinated.
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Emperor Franz Joseph of Austria-Hungary declares war on Serbia.
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The Ottoman Empire signs a secret alliance with Germany agreeing to enter the war once Germany declares war on Russia.
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Treaty of Brest-Litovsk is signed between Russia and Germany
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Germany declares war on neutral Belgium and invades Belgium and Luxembourg as part of the Schlieffen Plan. As a result, Britain declares war on Germany.
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Austria-Hungary declares war on Russia.
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The United States declares neutrality in the war.
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The German army defeats Russia at the Battle of Tannenberg.
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the German invasion of France is halted at the First Battle of Marne.
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The Race to the Sea ends when the Germans withdraw at the 1st Battle of Ypres.
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Unofficial Christmas truce is declared by German and Allied soldiers in the trenches along the Western Front.
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The Germans use poison gas at the 2nd battle of Ypres.
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Armenian Genocide begins.
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Allies begin a nine-month battle for the Turkish peninsula of Gallipoli.
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A German U-boat sinks the Lusitania killing 1,198 civilians, including 128 Americans.
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Italy Joins the Allies.
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British nurse, Edith Cavell, is executed by the Germans.
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The British introduced the tank during the Battle of Somme. The battle resulted in an estimated one million casualties.
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Woodrow Wilson is re-elected President of the United States.
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The Battle of Verdun was fought resulting in an estimated one million casualties.
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The Germans resume unrestricted submarine warfare.
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Tsar Nicholas II of Russia abdicates.
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The 3rd battle of Ypres, also known as Passchendaele, resulted in minor gains for the Allies and a total of 700,000 casualties.
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The Balfour Declaration is presented in London.
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President Wilson asks the U.S. Congress for a declaration of war against Germany.
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President Wilson outlines his Fourteen Points in a speech before Congress.
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British cryptographers deciphered a telegram from German Foreign Minister Arthur Zimmerman to the German Minister of Mexico
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Germans on the banks of the Marne near Paris are stopped by American forces at Chateau-Thierry
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Kaiser Wilhelm II of Germany abdicates.
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At eleven o’clock on this day, war on the Western Front ends as Germany and the Allies sign an Armistice.
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Germany and Allies sign the Treaty of Versailles. The U.S. Senate later refuses to ratify it.
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The Treaty of Sevres ends the war on the Eastern Front with the Ottoman Empire.