21 Solomon conscripted the descendants of all these peoples remaining in the land—whom the Israelites could not exterminatea —to serve as slave labor, as it is to this day.

Read 1 Kings 9:21 Using Other Translations

Their children that were left after them in the land, whom the children of Israel also were not able utterly to destroy, upon those did Solomon levy a tribute of bondservice unto this day.
their descendants who were left after them in the land, whom the people of Israel were unable to devote to destruction--these Solomon drafted to be slaves, and so they are to this day.
These were descendants of the nations whom the people of Israel had not completely destroyed. So Solomon conscripted them as slaves, and they serve as forced laborers to this day.