The US declared independence in 1776 and had the unification civil war in 1861. The political process is very gradual and even if a divisive issue such as slavery would pop-up in the EU then I doubt it would escalate into civil war. The EU has a lot of scar tissue related to wars.

If you consider that the US took 4 generations to unify and you consider that present-day it is hard to imagine a peaceful unification then you should also consider that the way you think about things is dramatically different then the way your grandchildrens' children will perceive things.

For example, currently a large part of the EU population speaks english as second language but it's hard to imagine that majority of voting-age EU population to not speak english as second language in 80 years from now.

Speaking a single language will probably clear the biggest hurdle for effective political union.