Hitler and Charlemagne were one of many who tried to unite Europe and recreate the old Roman Empire. Prophecy states that the divisions of the Roman Empire (Europe and the Byzantine Empire) will never unite to form another Roman Empire. It specifically mentions attempts to unite through families.
Among many other leaders throughout history Hitler and Charlemagne tried to unite Europe. They both meant to recreate a Roman empire. No one has yet been able to recreate such a union between the European countries like the Caesars did.
The Queen Victoria along with many other royal families have tried to unite Europe by marriage between royal families.
One of the most successful Unions was done by the church who was able to unite in some manner the European countries, but no attempt has been entirely successful.
Expansion of Empires Conquest of European empires and trade routes