Question

during the 1930s the united states followed a foreign policy of isolationism. which is the best example of that policy?
forbidding americans to travel overseas
building up the nations armed forces
avoiding alliances with other nations
favoring great britain over the rising power of nazi germany

Explanation:

Isolationism in foreign policy means a country tries to stay out of the affairs of other countries. Avoiding alliances is a key aspect as alliances involve getting involved with other nations. Forbidding travel isn't a typical isolationist policy (as trade and some exchanges might still happen). Building up armed forces could be for defense but not the core of isolationism. Favoring one nation over another shows some engagement rather than isolation.

Answer:

avoiding alliances with other nations