Final answer:
Isolationism, the belief in non-involvement in foreign affairs, inspired the idea that the United States should avoid involvement in world affairs.
Step-by-step explanation:
The idea that inspired the belief that the United States should avoid involvement in world affairs was isolationism. Isolationism is the policy of staying out of foreign entanglements and keeping to oneself. This idea can be traced back to the early days of the United States, with Thomas Jefferson being a strong advocate of non-involvement in foreign affairs. The quote from George Washington to 'avoid foreign entanglements' also contributed to this belief.