Germany (WWII), Japan (WWII), and US (Vietnam war) all had pacifist movements spring up in the aftermath of conflict. See also the aftermath of the regimes of Franco, Mussolini,and Ceausescu for domestic resets, just from the 20th century.

All in the 20th century. I attribute the fact that the US and Russia didn't head into a hot war post-WWII to the clear-headedness of witnessing WWII.