You could have given the same arguments 50 years ago to say Europe would never have a successful political union, continent-wide military alliance, or currency, and today they have all three.

Incidentally, I don't know about "a lot". Many European countries formed as unions of smaller states not that much longer ago than the colonization of America--the UK, Spain, Italy, and Germany all formed this way, Germany after the United States and the UK only a couple decades before. And nearly every country on the continent of Europe has already had its constitution rewritten within the past century.