The event that led to united states involvement in world war i was: the assassination of archduke ferdinand england's declaration of war the bombing of the maine germany's sinking of american supply ships

The correct answer is: "Germany's sinking of American supply ships".

The US managed to stay out of WWII until 1917 although, until that moment they have been sending supplies to the Allied forces. When Germany used submarines to bomb the supply ships, president Wilson had no option but to declare the war to Germany and to become part of the Allies or Entente countries that were figthing together the Triple Alliance.  

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