Essentially all of the industrialized world was destroyed in WWII, except the US. Being the only major supplier of manufactured goods for, the entire world resulted in a huge amount of economic growth that we coasted on for half a century.

Yes. Production peaks but what both the Nazis and FDR proved is that deficit spending is the surest way out of a massive recession if the spending goes into infrastructure and manufacturing. It is, quite literally, just an investment at that point. The production creates jobs, the jobs pay wages, the wages create more demand. This cycle then reaps benefits for decades if your factories don't get bombed to shit.

That said, this isn't the 1930s.

Even if WW3 doesn't end with a nuclear exchange it would still kill the planet as we throw every carbon limit out of the window.