What event led to U.S. involvement in World War I?

The U.S. involvement in World War I was primarily influenced by a combination of significant events, which includes the sinking of the Lusitania and the revelation of the Zimmermann Telegram. The sinking of the Lusitania, a British passenger liner, by a German U-boat in 1915 resulted in the loss of American lives and heightened anti-German sentiment in the United States. This incident played a crucial role in shifting public opinion toward supporting intervention in the war.

Simultaneously, the Zimmermann Telegram was a secret communication sent by Germany to Mexico, proposing a military alliance against the United States. When this telegram was intercepted and made public, it further inflamed tensed relations between the U.S. and Germany, solidifying the call for war. Together, these events created a compelling impetus for the U.S. government to join the conflict, marking a turning point that led to American troops entering the war in 1917. Thus, C is correct as it encompasses the pivotal events that directly led to U.S. engagement in World War I.