3. What is proof that the U. S. was not isolationist after wwi?

They sought a policy of isolationism? so they were isolationists wdym

Beginning with George Washington's presidency, the United States sought a policy of isolationism and neutrality with regards to the internal affairs of other nations. Early American political leaders argued that with the exception of free trade, self-defense and humanitarian emergencies, the U. S. would do best to avoid permanent alliances that do not serve American interests but instead deflect attention from domestic issues. When World War I broke out in July 1914, the United States actively maintained a stance of neutrality, and President Woodrow Wilson encouraged the U. S. as a whole to avoid becoming emotionally or ideologically involved in the conflict. Americans were more than happy to stay out of the war, and Wilson won a second Presidential term in 1916 by running on a platform of non-interference; the phrase, "he kept us out of war" became a popular slogan used by Wilson's supporters.

The easier answer is that they got involved in many more wars