"It has become this truism that we are stronger together. No, we are not. Europe conquered the world, because we were divided. Our strength came from our division not our unity.

Random events always happen. Every country will always experience a random bad leader. It will happen sooner or later. What is best then to have a land area unified into one or split into 10 different countries? One bad leader among 10 occasionally will not pull the whole area down. One bad leader for the whole area can pull the whole area into the dark ages.

Consider the Chinese emperor which banned all Chinese naval exploration and trade? That could never happen in contemporary Europe, because if your country got such a dumb leader your neighbors would quickly outcompete you and it would become very obvious how stupid that decision was within short time.

Being political divided is thus a good insurance against doom. Imagine someone like Hitler rising to power in a unified Europe? There would be no way to counter his madness."