The simple yet powerful consistency of history. Every time a group of humans, sometimes a minority, sometimes a majority, thought that surely the next X generation(s) will be more utopian than now - it always, always comes crashing back to more ethnic divide, factionalism, and war. And since you're using Europe as an example, no - they are not more united now than WWII era 70+ years ago. They aren't less united, but not more. Just different. Back in WWII era, Europe lacked monetary unification but had fairly specific national identities, more homogenous populations that may have bickered as a local family but even without the EU, acted as a block on many occasions. They now have a monetary union and more coordination for geopolitical negotiation to favor the EU block as a whole, but far more factionalized with new immigrants and far less homogenous populations that is leading to the strife we see re: national identities re-emerging in each euro country. And as shown by the Greece default, the EU is far less united in how to deal with the issue that will just get broader over time - the haves vs have nots, the inclusion of member countries that identify themselves as part of the EU but not as Europeans (e.g. Greece, Bulgaria, etc). TL;dr - what makes you think the 100% track record of history for continuing ethnic and geopolitical divide over time will not continue?