Ww2 started because everyone bent over for the Germans and Japanese, which encouraged them
This is extremely simplified and comes off as silly. German appeasement was partially because France and Britain wanted Germany to attack the USSR, partially because they needed time to rearm. The US empire had a policy of provocation and containment of the Japanese empire.
In the era of nuclear powers wars are done with non nuclear proxies to avoid a nuclear exchange.
WW2 was pre-nuclear weapons. It turns out that changing material conditions makes old responses inappropriate.