Answer:
To stop attacks on American people.
To avoid direct attacks on the United States.
Step-by-step explanation:
These were the two reasons that made America abandoned neutrality and join the war in the two world wars.
In World War I the declaration of war by President Woodrow Wilson was made after a scandal originated by a letter sent to Mexico by the German Foreign Minister Zimmerman. The letter tried to convince the government of Mexico to begin a war with German support against the United States to regain the territories lost in the Mexican-American War. The message was intercepted by Britain's intelligence and delivered to the American government. That was the last push needed to give up and neutrality and entered the war. The United States joins the war to avoid direct attacks on the United States.
In World War II the direct attack happened in Pearl Harbor and let many casualties. So the argument of the United States to join the war was to stop attacks on American people.
I hope this answer helps you.