Isolationists were people who believed that Americans should focus on American business and should not meddle in European affairs. This sentiment was especially strong around the two world wars when many people wanted the United States to stay out of the wars and lead the country alone and solve their own problems.
The answer would be an Isolationist. When you think about it, isolate means no involvement, so that would make sense because this is what the question is about. :) Hope it helped!
