I think the United States had a major role but they are rapidly losing power. Whether that is a good thing or not we don't yet know. It depends on whether the next power is as benevolent as its predecessors, Britain and the US.not recently. Not Syria -a regional proxty war, that we almsot stumbled into.
Such is the danger of thinking the US always has a role to play -we don't
You explained the problem in the first sentence. You enter a war to defeat your opponents and that's it. Once they are totally and absolutely defeated then you assist on nation building. Neither Churchill nor FDR would have announced a 'withdrawal date' during WWII and yet we've come to accept that nonsense as normal.I don't know how else to have fought Afg. we picked the counterinsurgency strategy, similiar to waht we did in Vietnam -commonly called "nationbuilding"
we cannot build outside societys, we can assist for a short term, but the danger becomes like Vietnam and Afganistan - long drawn out wars which leave those countries dependent on US forces to succeed.
And yet Cuba remains communist with millions dead and yet still receiving support from many leftists. It's just amazing and depressing how little mankind has advanced when we still support that sort of thing.Cuba was much more relevant to the US, even there the Bay of Pigs was badly played, though JFK recovered nicely during the Cuban missile crisis.