War, neither a milchemet hareshut or a milchemet mitzvah, should not be waged against anyone until they are offered the opportunity of peace as Deuteronomy 20:10 states: 'When you approach a city to wage war against it, you should propose a peaceful settlement.'
If the enemy accepts the offer of peace and commits itself to the fulfillment of the seven mitzvot that were commanded to Noah's descendents, none of them should be killed. Rather, they should be subjugated as ibid.:11 states: 'They shall be your subjects and serve you.'
If they agree to tribute, but do not accept subjugation or if they accept subjugation, but do not agree to tribute, their offer should not be heeded. They must accept both.
The subjugation they must accept consists of being on a lower level, scorned and humble. They must never raise their heads against Israel, but must remain subjugated under their rule. They may never be appointed over a Jew in any matter whatsoever.
The tribute they must accept consists of being prepared to support the king's service with their money and with their persons; for example, the building of walls, strengthening the fortresses, building the king's palace, and the like as I Kings 9:15-22) relates: "This is the tribute which Solomon raised to build the House of God, his own palace, the Milo, the wall of Jerusalem,... and all the store-cities which Solomon had... All the people that remained from the Amorites... upon them did Solomon lay a tribute of bondservice until this day."
In contrast, Solomon did not make bondsmen out of the children of Israel. They were men of war, his personal servants, his princes, his captains, the officers of his chariots, and his horsemen.