What would be the best historical example that you can think of? To be specific, what is a historical example of when a country would have benefited from expanding an empire, had the resources and ability to do so, and chose not to for an extended period of time?

That would be a strange form of communism.

Human greed is a base desire that has been a constant throughout our entire history. At some point, you're arguing for a fantasy. Either Communism is a realistic political system that can be implemented with humans as we are, including all of our base animal impulses, or it's a fantasy that requires humans to achieve a higher level of consciousness first or something.