When the Philistines heard that David had been anointed king over Israel, all the Philistines went up to search for David. But David heard of it and went down to the stronghold. Now the Philistines had come and spread out in the Valley of Rephaim. And David inquired of the Lord, “Shall I go up against the Philistines? Will you give them into my hand?” And the Lord said to David, “Go up, for I will certainly give the Philistines into your hand.” And David came to Baal-perazim, and David defeated them there. And he said, “The Lord has broken through my enemies before me like a breaking flood.” Therefore the name of that place is called Baal-perazim. And the Philistines left their idols there, and David and his men carried them away. 2 Samuel 5:17-21.
These are good times for David. After Ish-bosheth is murdered, the Israelites submit themselves to David without a fight. The King of Tyre recognizes his government and contributes timber toward the new palace. David takes Jerusalem and new wives and concubines. He is still inquiring of the Lord about battle plans, and the Lord us giving him victory.
In the instructions the Lord had written for kings, one of those was not to take many wives, especially foreign wives, who might entice you to worship their gods. So, how many is too many? God was not specific, although it was not uncommon for any man who could afford to support them to have several wives and/or concubines.
Concubinage was a fairly normal arrangement in ancient times. Brute force was the engine of wealth at that time, and it favored men. There was not a viable path to independence for women. It would be centuries before specialization infrastructures would make it possible. So at this time a woman who was not able to get a husband of her own could become an extension of a wealthy man’s household and raise her children in peace and safety. There are women in America today who might find this is a better deal than section 8 housing and food stamps.