The correct answer is the following.
Before World War II, the United States focused its expansionist policies on expanding its territories to create a stronger country. The United States was not a major imperialist nation as it was Spain of the United Kingdom, but indeed fought wars against Spain in the Spanish-American War for the Philippines and the island of Cuba. After the U.S. participation in World War 1, the United States changed its foreign policy and decided to isolate themselves from the world. It refused to participate in the League of Nations and focused mainly on U.S. issues. Then it came the attack on Pearl Harbor in 1941, and the U.S. military was not strong enough to respond alone to the attacks. He joined the Allied Forces with Great Britain and the Soviet Union to fight the Power Axis.
After World War II, the United States modified its foreign policy 180 grades. It was the leading nation in forming the United Nations, formed NATO (North Atlantic Treaty Organization) to protect its interest and those from its allies, and supported the Marshall Plan to help reconstruct damaged European nations after the war. During the Cold War period, the U.S. tried to stop the spread of Communism in many regions of the world, including strategic territories in Central and South America. After the 9/11 attacks, the U.S. strengthen its combat to terrorism, created Homeland security and permanently look for its interest in the Middle East.
