Are Americans imperialists or isolationists? Whether the United States should intervene and lead, or show global restraint, is a recurring theme of US foreign policy, argues Stephen Kinzer. This debate may be more pertinent now, as President Trump formulates his global strategy. From the imperialist invasions of the 19th and 20th centuries, to the more recent interventions overseas, any action the United States takes has major global reverberations. Why has the United States oscillated between intervening and restraining in an increasingly complex international system? What does the past tell us about our future?