I assume your talking about the HUNS... When the empire split in two the east had more gold and more resources and the dying west had to suffer all the barbarian attacks like the huns... The East quite simply was more prepared and had more walls and guards to defend their border also the Eastern Empire had the river danube north of them which helped deflect the Hunnic invasions and other barbarian invasion more west...
The core Idea was manifest destiny. God gave us power so why not use it? Whenever we kicked mexico's behind we realized we could really accomplish this ambition
