what event ultimately led the united states to change its foreign policy

There isn’t a single, definitive event that caused a permanent shift in U.S. foreign policy. However, historians often point to American entry into World War I (1917) as a major turning point.

Prior to WWI, the U.S. generally followed a policy of isolationism, avoiding entanglement in foreign conflicts. WWI’s devastation and the rise of Germany as a global power convinced many Americans that isolationism was no longer sustainable. The U.S. emerged from the war as a major world power, and since then has played a more active role in international affairs.