Explanation: It was because of WW1, it was due to the many casualties that America suffered in WW1. The United States did not want to interfere with other countries' political affairs during the war but they did at the very end. They joined in and had "open door policy" and remained neutral in the war. Afterward, America did not experience as much of a devastating loss from WW1 but they decided to seclude themselves to repair themselves after the war. Ironically, they experienced an economic boom and prospered. Partially due to the war and a shift into a new decade. However, all good things must come to an end. By the end of the 1920s, the Great Depression kicked in. Economic devastation flooded other countries aswell. Since other countries were also experiencing a depression, trade slowed down and communications to other countries slowed down. This also contributed to isolationism before WW2. Luckily, in the beginning of WW2, America decided to isolate itself once again. This was however disrupted due to Pearl Harbor. WW2 ended up helping America get out of the Depression and was one of the reasons why America decided to participate in the war.
