The Haftarah for Parshas Chukas, sourced from Shoftim (11:1-33), is deeply connected to our parsha as elucidated by the Levush (549:1).
Our parashah concludes with Moshe's triumphant battle against the people of Amori. The Jews emerged victorious, seizing both the land and the land of Moav. The Haftarah, in turn, narrates the subsequent war waged against the Jews three centuries later in an attempt to reclaim the land of Moav.
The Jewish leader, Yiftach, tried to make peace, but the king refused, and they attacked the Jews. Yiftach vowed that whatever emerges from his house first will be offered as a sacrifice if he wins the war.
When he arrives home, his only daughter emerges from his house, leaving him with a dilemma about fulfilling his vow. Midrash (Bereshis Rabbah 60:3) discusses how one deals with such a vow: either to redeem it with money, or the vow isn't valid to begin with because a person is not a valid Sacrifice.
The Haftarah ends with him winning the war.