Matthew Poole and continuators on 1 Kings 9:21

21 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 bond-service unto this day.

He used them as Bond-men, and imposed Burdens and Bodily Labours upon them. See 2 Chron. 2. 18. Hence some think they are called Solomon's servants, Ezra 2. 55, 58. Quest. Why did not Solomon destroy them, as God had commanded, when now it was fully in his power to do so? Ans. First, The command of destroying them, Deut. 7. 2. did chiefly, if not onely, concern that Generation of Canaanites who lived in or near the time of the Israelites entring into Canaan. Secondly, That Command seems not to be Absolute and Universal, but conditional, and with some exception for those who should submit to them, and embrace the True Religion, as may be gathered both from Ios. 11. 19. and from the History of the Gibeonites, Ios. 9. whom Ioshua did not sin in sparing, when he had Sworn to do so; and Saul did sin in indeavouring to destroy them. But if Gods Command had been Absolute, the Oaths of Ioshua, and of the Princes, could not have obliged them, nor dispensed with such a Command.

Marginal references: Judg. 1. 21, 27, 29.