I admit that the US probably should have gotten involved sooner in WW IIAfter years of hardship, US people were concerned about their own wellbeing rather than a war on distant fields. Which is fair enough. The days when an enemy can sneak across your borders with a WMD or reach around the globe to strike you from afar, had not yet arrived.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1