What is an isolationist in social studies?

The doctrine that a nation should stay out of the disputes and affairs of other nations. The United States practiced a policy of isolationism until World War I and did not pursue an active international policy until after World War II.

Other def: a policy of remaining apart from the affairs or interests of other groups, especially the political affairs of other countries.

Isolationism is basically where a country or group chooses to remain apart from foreign affairs and issues politically, so an Isolationist is a person or party who practices Isolationism.