Eastern Europe is still warring over land - Bosnia is basically part of Europe. Yes that would mean Civil War in Europe. These areas need sorting out - vast numbers of our troops being there is NOT an answer. Look at the amount of paperwork generated by a partial union of Europe. We will be SUNK by bureaucracy.
Bureaucracy means more expense.
An economic and social mess. Communism does not work. Russia proved this. Human nature runs against Communism and it fails, spectacularly. CAP - Common Agricultural Policy is one example.