What was President's Roosevelt impact on U.S. foreign policy?
He made the U.S. a world power.
After WW1, the U.S. slipped back into an isolationist mode. The army went to a low of 130,000 troops and the Navy was largely a group of aging relics sitting in the ports of Norfolk, San Diego and Honolulu.
When Germany invaded Poland, September 1, 1939 and soon thereafter attacked Great Britain, Roosevelt realized that even though he had promised the American public he would not partake in foreign (European) wars, he knew we would ultimately be dragged into the conflict one way or another.
Roosevelt's "Lend-Lease Act" was the first step in bringing America back onto the world stage. His meetings with Stalin and Churchill are legendary.