Final answer:
America's entry into World War I was influenced by German unrestricted submarine warfare, the Zimmerman Telegram, and the protection of economic interests, not by events occurring after the conflict began.
Step-by-step explanation:
The three situations that led to America's entry into World War I were not the signing of the Armistice, the League of Nations formation, nor the Paris Peace Conference, which all occurred after the U.S. had already entered the conflict. Instead, the United States entered the war due to factors such as unrestricted submarine warfare by Germany, the Zimmerman Telegram, and a need to protect U.S. economic interests.
Specifically, Germany's unrestricted submarine warfare, which included the sinking of the Lusitania, threatened American lives and shipping. The Zimmerman Telegram, a message from Germany to Mexico proposing an alliance against the U.S., was intercepted and outraged the American public. Lastly, the U.S. had significant economic investments in the Allied powers that could be jeopardized if the Allies were defeated.