Islam made caste problem acute !
Just imagine the scene. The king has been defeated and killed by the Islamic invaders.There is rape,murder,loot all around and there is no one to save or impose social order. People flee to save their life ,property & honour to remote corners.Where ever such people settle, per force have to be self sufficient. Now suppose there is only one potter .No one else knows the trade.After the potter’s death , the community will naturally force the son/sons to be potter.Thus castes became rigid.