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        The heir to the Austro-Hungarian throne was killed in Sarajevo by Gavrilo Princip, sparking tensions that led to war. - 
  
  
        This marks the official beginning of World War I as alliances between nations begin to activate. - 
  
  
        Germany supports Austria-Hungary, while Russia backs Serbia, escalating the conflict. - 
  
  
        Germany launches its plan to quickly defeat France before turning to fight Russia. - 
  
  
        Britain joins the war after Germany violates Belgian neutrality. - 
  
  Germany defeats Russia in one of the first major battles of the Eastern Front.
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  Allied forces stop the German advance on Paris; trench warfare begins.
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        Germany uses chlorine gas for the first time, introducing chemical warfare. - 
  
  Allied forces attempt to control the Dardanelles but fail against the Ottoman Empire.
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  One of the longest and bloodiest battles; symbol of French determination.
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  Over one million casualties; tanks used for the first time in combat.
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        Fought in terrible muddy conditions; heavy losses for small territorial gains. - 
  
  The Tsar is overthrown, and later, the Bolsheviks seize power under Lenin.
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        The U.S. joins the Allies, bringing new troops and resources to the fight. - 
  
  The Allies launch a final series of attacks that push German forces back.
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        Russia officially withdraws from the war after peace talks with Germany. - 
  
  
        Fighting stops at 11 a.m.; Germany agrees to ceasefire, ending World War I. - 
  
  
        Officially ends the war; Germany is blamed and forced to pay reparations.