The Ottoman empire caused tons of Muslim migrants to enter its core provinces. Empires always managed and reshaped migration. The Romans resettled conquered peoples across their empire to strengthen borders and repopulate cities. The Habsburgs moved ethnic groups into borderlands against the Ottomans. The Russian Empire orchestrated mass movements of Tatars, Circassians, and others. In all these cases, imperial expansion created migration streams that later fed into demographic and political conflicts.