That's putting the cart before the horse; countries only join the EU after they're already politically aligned with the current membership. Turkey, for instance, has been kept out of the European Union precisely because of these types of concerns; a strategy of economic integration would have entailed allowing Turkey to join the EU in hopes that the EU would be a positive influence on the country.

Edit: I'm being throttled so I'll respond to similar comments here. TheOtherHobbes similarly notes:

> The EU. France and Germany used to be deadly enemies. No one sane is expecting a war between them any time soon.

In particular, France and Germany weren't peacefully reconciled through economic integration. There was a war, and the victors of that war installed democratic governments in both France and West Germany and inducted both countries into a broader alliance.

> Same with US states. Texas etc keep muttering about secession, but the economic complications make it an insane idea.

It took about two decades after Texas was admitted to the union for the states to fight a civil war against each other.

genman says:

> Remember WW1? WW2?

Not personally (I'm not that old) but those were not instances of economic integration easing military tensions; they were instances of extremely bloody world wars. And the First World War in particular was already deemed impossible because of the degree to which European economies were already economically integrated. That theory did not pan out.

wolverine876:

> The EU (in its early forms) was formed by the countries that just fought each other in WWI and WWII, and for centuries before that. The EU was specifically intended to prevent another war.

Again reversing cause and effect. The Allies won the Second World War and installed friendly governments across western Europe (and also in Greece); following this, those friendly governments formed the EU.