It only happened after WW2 because the US came out of that war as the only untouched developed economy. A WW3 isn't going to leave anyone unscathed and would probably mean all-out nuclear war.
I think a bigger factor is how the war broke up a lot of the old power structures and for a couple of decades it was really possible to get ahead even if you started off poor. There was an abundance of need for labor rebuilding the world and servicing the sudden boom in consumer goods that arose from all of the technologies being developed. Those power structures have reformed and now we are back in the neofeudalism model that arises when power is allowed to ossify.
There is no guarantee that a WW3 would even repeat this phenomenon.
US feared people from ravaged countries would embrace communism, and showered them with cheap cash for jobs and reconstruction. Unfortunately capitalism today faces no competition, and it's devolving into techno-feudalism. The super-rich have a hard time sharing wealth with the rest of us, in absence of credible threat of some revolution putting their heads to the guillotine or something like that.
WW2
>What Would It Take to Have Another?
WW3