Or they want to make it never happen again so they institute hundreds of bureaucratic processes that only a select class of insiders have the ability to navigate, thus forming the political power bottlenecks which will lead to the corruption and waste that sparks the next war.
The EU itself is likely still very far from starting that war. China and its superiority complex seems much more likely if they can find someone willing to stand up to them. Or maybe Russia is going to overstep its boundaries for real sometime. Either way we're probably close to our 80 or so years of "Western" (relative) peace, certainly fear and populism are not helping to avoid that path.