After looking at http://geacron.com/home-en/ and looking at all the Empires that dominated the the fertile crescent, I came to be reminded that Rome was the first and most succesful Empire in uniting Europe.
But were they really the first? I heard that the Celts were supposed to be all over the place. So really, was there anything that can be compared to the Roman and mesopotamian Empires in Europe?
No. There were many smaller kingdoms before the roman empire that held relatively large amounts of territory but none came close to controlling as much territory as the Romans. The Macedonian Empire for a very brief time controlled as much territory as the Roman Empire, but almost all their territory was in the Middle East and it collapsed as soon as Alexander died. As for the Celts, the Celts did indeed spread across much of Europe but they were a people/cultural group not a political entity. There was never a celtic kingdom that spanned from Ireland to Turkey it was hundreds of different tribes that shared a similar culture and language.