IIRC Rome actually had a pretty good system for this, where they defeated any large migrating tribes in battle (even if it was kind of a joke battle, a lot of t

IIRC Rome actually had a pretty good system for this, where they defeated any large migrating tribes in battle (even if it was kind of a joke battle, a lot of them were fleeing from other forces that had already drove them out) and then disarmed and spread the families out into different provinces. This broke the large potentially dangerous group up and kind of forced them to integrate into the roman system instead of being a different entity inside the empire. It didn't even really stop working, some bad leaders were just to lazy to do it towards the end.