I remember reading an analysis of (I believe) WWI that said that by that point, the rulers of Europe had successfully completed the hard work of discouraging war among themselves through a long-term project of intermarriage. They were all related to each other and therefore mostly uninterested in going to war against each other.[1]
But at some point popular demand for war started to rise and the noble houses weren't able to stop it.
We're seeing something similar here.
[1] This can't be the whole story; European history is replete with brother-brother and father-son wars. But I think the idea is worth considering anyway.