Although renowned political scientist John Mearsheimer does not consider himself to be an isolationist – a term which has acquired a negative connotation since WWII – his definition is illuminating as much for clarifying what the term does not mean as for what it does.
In America Unhinged, Mearsheimer writes: “Isolationism rests on the assumption that no region of the world outside of the Western Hemisphere is of vital strategic importance to the United States. Isolationists do not argue that America has no interests in the wider world, just that they are not important enough to justify deploying military force to defend them. They are fully in favor of engaging with the rest of the world economically as well as diplomatically, but they view all foreign wars as unnecessary.”
As Mearsheimer makes plain, isolationism does not constitute a lack of constructive engagement with the outside world, but a judicious engagement that eschews military action outside of defending the homeland.