Size is important. I think everything gets harder with increased size. The more I look at the US, the more I like the EU being more of a confederation than a union, even though all the horse trading makes Brussels a mess. Countries with homogeneous culture and a population less than 10 million just seems optimal. There are positive scaling effects to be had, and I don't think the EU is quite strong enough to capture them all yet, but I think a vision of a USE is misguided.