In Shoftim (Judges) 21, the tribe of Benjamin was almost eliminated except for 600 men. However, all the other tribes had made an oath stating that no one was allowed to give their daughters to the men of the tribe of Benjamin:
מַה־נַּעֲשֶׂ֥ה לָהֶ֛ם לַנּוֹתָרִ֖ים לְנָשִׁ֑ים וַאֲנַ֙חְנוּ֙ נִשְׁבַּ֣עְנוּ בַֽיהוָ֔ה לְבִלְתִּ֛י תֵּת־לָהֶ֥ם מִבְּנוֹתֵ֖ינוּ לְנָשִֽׁים׃
How shall we do for wives for them that remain, seeing we have sworn by the LORD that we will not give them of our daughters to wives?’
Why couldn't the other tribes get their oath / vow annulled?