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Germany invades Belgium and France, leading Britain to declare war on Germany.
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The First Battle of the Marne halts the German advance into France, marking the beginning of trench warfare on the Western Front.
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Archduke Franz Ferdinand of Austria is assassinated by a Serbian nationalist.
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Austria-Hungary declares war on Serbia, triggering a network of alliances and beginning World War I.
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Allied forces land on the Gallipoli Peninsula in an attempt to capture the Ottoman Empire's capital, an ultimately unsuccessful campaign.
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A German U-boat sinks the British passenger liner Lusitania, killing many Americans and increasing anti-German sentiment.
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The Battle of the Somme begins, a four-month offensive with huge losses for all sides and little strategic gain.
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Germany begins the massive and brutal Battle of Verdun, a six-month engagement with horrific casualties.
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The United States enters the war after Germany renews its submarine warfare.
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Russia withdraws from the war after signing the Treaty of Brest-Litovsk with Germany.
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The Battle of Amiens and the Meuse-Argonne Offensive result in a decisive Allied victory, pushing back the German forces.
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Germany launches the Ludendorff Offensive, a final attempt to win the war, but the Allies respond with their own offensives.
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An armistice is signed, bringing an end to the fighting on the Western Front.