In the opening verses of Judges 10 we read about a couple of Israel's leaders and no mention of whether or not they were obedient to the Lord.  Then beginning with verse 6 we find that the Israelites are once again doing evil in the eyes of the Lord.  It mentions several gods including Baal and Ashtoreth and other gods who were similar gods but with different names.  Baal was the god of the harvest and Ashtoreth was the goddess of sex.  The god Chemosh mentioned in Judges 11 was the national deity of the Moabites and a god of the Ammonites, also identified with ‘Baal-peor’, ‘Baal-zebub’, ‘Mars’ and ‘Saturn’.

Because the people served these false gods, the Lord sold them into the hands of the Philistines and the Ammonites. (The Ammonites were descended from Ammon, Lot's son by his daughter).  Israel was in great distress because of their disobedience in following other gods.

Gilead is a mountainous region bounded on the west by the Jordan, on the north by Bashan, on the east by the Arabian plateau, and on the south by Moab and Ammon; sometimes called ‘Mount Gilead’ or the ‘land of Gilead’ or just ‘Gilead’. Divided into north and south Gilead.

Stories in the Bible don’t always have a “happily ever after” ending. The story of Jephthah and his daughter is one of those stories that is both shocking and confusing. Jephthah made a rash bargain with God. If God would allow him victory against his enemies, he would sacrifice the first thing that came out of his house. Unfortunately, it was his daughter that came out of the house to meet him. How could a man make such a promise? Equally shocking and confusing is that Jephthah’s daughter also honored her father’s bargain.

When Jephthah told his daughter about the bargain he had made with God, she asked to be allowed two months to roam the hills and weep with her friends.  Did Jephthah think that she might run away to a distant land and he wouldn't have to sacrifice her?  Also, did he think that God would stop the sacrifice of his daughter the way He stopped the sacrifice of Isaac by Abraham?  Notice that the girl returned to her father willingly.

What does God say about such a bargain as Jephthah made?
Eccl 5:4-6a
When you make a vow to God, do not delay in fulfilling it. He has no pleasure in fools; fulfill your vow. It is better not to vow than to make a vow and not fulfill it. Do not let your mouth lead you into sin.

Leviticus and Deuteronomy list rules pertaining to vows of dedication.
Deut 23:21-23
If you make a vow to the LORD your God, do not be slow to pay it, for the LORD your God will certainly demand it of you and you will be guilty of sin. But if you refrain from making a vow, you will not be guilty. Whatever your lips utter you must be sure to do, because you made your vow freely to the LORD your God with your own mouth.

This passage is very clear that such vows like the one that Jephthah made are not from the Lord. They are from the mouth of men. Lessons for us are equally clear. We must be very cautious in making vows to the Lord.  But when we make a vow, we'd better keep our end of the bargain.