en_tn_lite_do_not_use/jdg/21/01.md

Now the men of Israel had sworn ... marry a Benjamite."

This background information tells the reader about the promise that the Israelites made before the battle with the Benjamites. (See: rc://en/ta/man/jit/writing-background)

Benjamite

This is the name of the descendants of Benjamin. See how you translated this in Judges 3:15.