Surely that can be better explained by the European countries being fatally weakened by WWII (there were plenty of European conflicts after WWI), which allowed the US and Soviet Union to become the two uncontested hegemons? They very much did not want their European buffer zones to reduce their effectiveness by squandering military resources on infighting, so they enforced that their militaries remain small and, more importantly, dedicated only to defense (while remaining available for the imperial adventure of the hegemons). Both the Soviet Union and especially the US (being the prototypical ocean empire) have found plenty of excuses to get involved with war with an eye to their own benefit. Meanwhile, the European militaries have rotted to the point where most barely have any weapons to send to Ukraine. (Eastern Europe, not being under the thumb of the US for as long and being closer to Russia, has retained a stronger military.)