Which war? WWI: We were isolationists until illegal German U-boats sank a United States commercial ship called the Lusitania.
WWII: We were isolationists until December 7, 1941 when the Japanese air fleet surprise attacked and bombed us at Pearl Harbor.
U dunno let me check the web for that one
Answer:
They were not discover that time so false
C they were devastated by european diseases.