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

The U.S. involvement in World War I was significantly influenced by the sinking of the Lusitania. In May 1915, this British ocean liner was torpedoed by a German U-boat, resulting in the deaths of nearly 1,200 passengers, including 128 Americans. This event caused public outrage in the United States and increased anti-German sentiment among the American populace.

The Lusitania was not just a commercial vessel but was also rumored to be carrying munitions, which intensified the perception that Germany was engaging in reckless and unlawful acts of warfare against neutral countries. This incident served to shift public opinion about the war and placed pressure on President Woodrow Wilson to take action against Germany, contributing to the decision to eventually declare war in April 1917.

While other options reflect significant historical events, they do not pertain to the United States' entry into World War I. The assassination of Archduke Franz Ferdinand initiated the conflict in Europe, but it was the direct actions of Germany, showcased by events like the Lusitania's sinking, that directly influenced U.S. involvement. The bombing of Pearl Harbor and the invasion of Poland are sequentially linked to World War II, not World War I.