Does the question make sense? The idea of a unified Europe is modern. Rome conquered Gaul, Serbia was in the Ottoman Empire, the Mongols traveled quite far west

Does the question make sense? The idea of a unified Europe is modern. Rome conquered Gaul, Serbia was in the Ottoman Empire, the Mongols traveled quite far west. The idea that Holland invading and capturing Britain meant different things then than it does now. Now they're both European nations. Then they were just two different nations. At least two books that provide hypotheses with some supporting evidence are: Guns, Germs, and Steel; and A Splendid Exchange. One thing that I found incredibly interesting in common was superior technology and the positive feedback loop with that. By this, I mean financial technology (loans, trade, financial derivatives) as well as weapons and mills.