Your comment still lacks more context why migration wasn't a big deal and why more decentralized power structure didn't need to control migration as much. 1. H

Your comment still lacks more context why migration wasn't a big deal and why more decentralized power structure didn't need to control migration as much. 1. Human labour was much more critical to survival than today. It was a great thing if one family from another town moved under you cause they'll farm and pay more taxes. Now labour is cheap and isn't critical survival. In fact, there's so much labour that social ills that arise from unemployment is a way bigger problem. 2. Migration happened in much shorter proximity. Therefore, the difference in language, culture, ethnicity and religion were much smaller than the effects of migration today. The host society wasn't concerned about huge changes of their society as much as today where changes of biblical scale are happen in a matter of decades. 3. There was no welfare. If you failed as a migrant, the cost of the failure is paid by yourself. If you fail as a migrant in the host society today, you still have free healthcare, education, citizenship for your children, child care, endless support system to sustain your living in the country. It makes sense the modern state wants control over who enters their state much more.