fdr had no choice but to get involved in world war two. trump is creating drama out of nothing.
america's success in that war and afterwards, was due as much to its sheer geographical isolation, as for any other reason; while america spent all kinds of the wealth it had tooling up its industries, and for the most part *not* getting bombed, various other major industrial powers were getting the literal s hit bombed out of their industrial infrastructures
they were not talking a lot of big, big crap on twitter, in those days, in other words
and the outcome of all this was of course that, in the end, america was left basically with complete ownership of the entire industrial economy, of the free world. an advantage they managed to avoid p issing entirely away, for whole decades afterwards.
you want to understand the current world economy? well, here's a clue: the rest of the world didn't sit on their a ss in the flaming rubble of their former cities forever, did they