Final answer:
The policy of neutrality and isolationism at the start of World War I and World War II eventually led to greater involvement and engagement by the United States in global affairs.
Step-by-step explanation:
The policy that the United States adopted at the beginning of World War I and World War II was one of neutrality and isolationism. At the start of World War I, President Woodrow Wilson aimed to maintain commercial ties with all belligerents while insisting on open markets throughout Europe. However, the United States eventually joined the war and Wilson presented his Fourteen Points as a plan for postwar peace.
In the period between World War I and World War II, isolationist sentiment returned as the idea emerged that Europe should govern its own affairs. However, after World War II, the United States became actively engaged in world affairs as a superpower and military leader.
Overall, the policy of neutrality and isolationism at the beginning of both wars eventually gave way to greater involvement and engagement by the United States in global affairs.