In a way, communism is an extreme form of socialism. Many countries have dominant socialist political parties but very few are truly communist. In fact, most countries - including staunch capitalist bastions like the U.S. and U.K. - have government programs that borrow from socialist principles. "Socialism" is sometimes used interchangeably with "communism" but the two philosophies have some stark differences. Most notably, while communism is a political system, socialism is primarily an economic system that can exist in various forms under a wide range of political systems.