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The objective of the assassination was to break off Austria-Hungary's South Slav provinces so they could be combined into a Yugoslavia.
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The Russian army move their vast military to intervene against the Austria-Hungary military. They do this to help their ally who is Serbia.
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Germany invades Belgium, starting World War 1.
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The German army fire shells filled with chlorine gas at allied lines. This is first time that large amounts of gas has been used in battle. Even with this the Germans were unable to get the advantage in the breach.
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A German submarine sinks the passenger liner Lusitania. The ship carried 1,198 people, 128 of them were Americans.
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Reacting to international outrage at the sinking of the Lusitania and other neutral passenger lines, Kaiser Wilhelm suspends unrestricted submarine warfare. This is an attempt to keep the United States out of the war, but it severely hampers German efforts to prevent American supplies from reaching France and Britain.
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The British employ the first tanks ever used in battle, at Delville Wood. Although they are useful at breaking through barbed wire and clearing a path for the infantry, tanks are still primitive and they fail to be the decisive weapon, as their designers thought they would be.
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Germany resumes unrestricted submarine warfare in European waterways. This act, more than any other, draws the United States into the war and causes the eventual defeat of Germany.
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British intelligence gives Wilson the so-called Zimmermann Telegram, a message from German foreign secretary Arthur Zimmermann proposing that Mexico side with Germany in case of war between Germany and the United States
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President Wilson outlines his case for war to Congress.
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Congress authorizes a declaration of war against Germany. The United States enters World War I on the side of France and Britain.
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Congress passes the Selective Service Act authorizing the draft. Although criticized for destroying democracy at home while fighting for it abroad, President Wilson claims he sees no other option and signs the bill into law.
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The Germans sign a peace treaty with the new Bolshevik government of Russia. The terms of the treaty give Germany huge tracts of land that had been the Ukraine and Poland, and peace on the Eastern Front.
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The Battle of Cantigny is the first major American offensive of the war. It gave America courage to fight German in larger attacks.
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The Americans attack the Germans at Chateau-Thierry. This battle would morph into the larger Battle of Belleau Wood.
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The Battle of Belleau Wood begins as the U.S. Marine Corps attacks the Germans across an open field of wheat, suffering huge casualties. It started June 6, 1918 and ended June 26,1918.
