What does Judges 21:18 mean?

This provides more details about the oath which prevents the other eleven tribes from quickly and easily providing wives to prevent the tribe of Benjamin from becoming extinct. Before the battle against Gibeah (Judges 20:11–13), when they were the most outraged at Benjamin's defense of the city, the Israelites had made a hasty oath (Judges 21:1). They had pledged themselves before God not to give their daughters to the men of Benjamin in marriage. The oath included the line that anyone who gives a wife to Benjamin will be cursed.

The Lord had instructed the people of Israel to take their oaths and His curses with deadly seriousness (Deuteronomy 23:21–23). They did not even consider breaking this oath, even after deciding that Benjamin must be saved instead of ended. No one bound by the oath can give a daughter to Benjamin. Neither can wives be taken from the Canaanites, or their children won't be true sons and daughters of Israel (Deuteronomy 7:1–5).

To solve the dilemma, Israel has already punished a clan who didn't support the war—and was not present to make the marriage oath—which provided wives for about two-thirds of Benjamin's survivors (Judges 21:8–14). To account for the remaining two hundred wives (Judges 20:47–48), Israelites will look for loopholes in their self-made trap.