Which policy did the United States adopt when World War I first broke out in Europe? A. isolationism B. militarism C. imperialism D. pacifism

A. isolationism

Explanation:

When the World War I broke out, the United States didn't planned to get involved in it. Initially, the United States considered this war to have anything to do with them, so they adopted a policy of isolationism. The reason for adopting isolationist policy was to protect its social, economic, and political interest. This quickly changed though, and the United States got involved in the second half of the war, so the isolationism was very short-lasting.