By the 18th century, immigration via indentured servitude had become much rarer than in the early to mid 17th century. It was cheaper in the long run and much less trouble to purchase African slaves. There were two big reasons for this. One, the indentured Englishman was still legally free, entitled to certain rights and privileges, and had legal recourse via colonial courts in the event of a dispute with his master. Two, most indenture relationships required the master to pay off the servant at the end of the contract, either with land or cash. This became a real problem as the colonies became more settled, producing a class of landless poor whites and blacks. In 1676, a group of them burned the Virginia capitol. That helped to put a damper on indentured servitude.

By purchasing the initially more expensive slaves, masters were guaranteed a permanent labor force with no recourse to law. This is basically how race slavery began in American history. Virginia tobacco planters in the early to mid 17th century slowly chipped away at the rights of African indentured servants, initially by having some sentenced to life indentures as a punishment for disobedience or rebellion, until by 1660 they had become effectively enslaved as a class.

They could not do this with white indentured servants. In the event of rebellious or runaway servants, masters could bring them before colonial courts, and if caught they might be sentenced to an extended term. A five year contract might become ten. A runaway could potentially try to get beyond the reach of these courts, but that would require going west to the frontier, penniless and without friends, and hoping no one ever recognized him. In the meantime, the master would be putting descriptions of him in every local newspaper along with a promise of reward for capture.

If I could add a second question, What would prevent my new masters from never releasing me from my contract?