During World War II, America's foreign policy shifted from a policy of isolation to one of intervention and engagement in global affairs. Before the war, America had followed a policy of isolationism, which meant they wanted to avoid getting involved in foreign conflicts and focused on domestic issues. However, the attack on Pearl Harbor in 1941 changed everything.
After the attack, America declared war on Japan, Germany, and Italy and became fully engaged in World War II. The U.S. was now committed to protecting its interests overseas and promoting democracy around the world. President Franklin D. Roosevelt articulated this new foreign-policy approach with his famous "Four Freedoms" speech in 1941.
During the war, the U.S. formed alliances with other countries, including the United Kingdom and the Soviet Union, and worked together to defeat the Axis powers. America provided military and economic aid to its allies and contributed significantly to the war effort.
At the end of the war, the U.S. emerged as a superpower, and its foreign-policy shifted towards containment and the prevention of the spread of communism. The Truman Doctrine, established in 1947, committed the U.S. to supporting free peoples who were resisting communism.
In conclusion, America's foreign policy changed dramatically during World War II. From a policy of isolation to one of intervention and engagement. The war led to the formation of alliances, increased U.S. involvement in global affairs, and the emergence of the U.S. as a superpower.