So, we have to set the wayback machine before the war on this one, which is exactly how chapter 21 of Judges begins. See, it feels the need to tell us some of the details regarding the (air quotes) “justice” (/air quotes) they swore against the Benjamites. In particular, the beginning of this chapter wants to call out how all of those who gathered to strike back against the Benjamites swore, “no one of us shall give his daughter in marriage to Benjamin.” Cuz, y’know, they done bad.
The reason that we need to know this now is because Benjamin is on the verge of extinction. There are 600 people left, the ones who ran to Rimmon. There are 12 tribes of Israel, not 11. And the rest kind of feel bad that “one tribe [is] lacking in Israel” as if it was just an unfortunate set of circumstances and that they had nothing to do with putting every Benjamite settlement to the sword, burning them nearly into extinction.
So they want to do something to help Benjamin out, but they’re not willing to do too much. After all, Benjamin did a bad, bad thing, and they don’t want to send any of their daughters into that. How do we solve this? How can they help Benjamin rebuild without violating their oath? By approaching those who did not swear the oath.
Not all settlements in Israel turned out to swear vengeance against Benjamin. The little settlement at Jabesh-gilead hadn't shown up. They either didn’t get the memo (re: the body part of the concubine), they were busy that day, or they just didn’t want to be part of annihilating a fellow tribe.
Actually, we have no idea why those at Jabesh-gilead didn’t show up. And we never will. That whole, “it got worse part,” well, here it is.
“Go, put the inhabitants of Jabesh-gilead to the sword, including the women and little ones” (Judges 21:10).
I’m just going to end here for now. We need to let that sink in.