God told them not to make a treaty with the people living in the land.
Exod 34:12-15
Be careful not to make a treaty with those who live in the land where you are going, or they will be a snare among you. Break down their altars, smash their sacred stones and cut down their Asherah poles. Do not worship any other god, for the LORD, whose name is Jealous, is a jealous God. "Be careful not to make a treaty with those who live in the land; for when they prostitute themselves to their gods and sacrifice to them, they will invite you and you will eat their sacrifices.

The people of Gibeon tricked Joshua into making a covenant with them claiming that they were from a distant country. Isn’t that just like Satan? He played on Joshua’s mercy. Even after Joshua realized that he had been tricked, he still wanted to hold on to the oath he had made with men rather than to please God. Not a good thing!

How often do we as Christians worry about what others think, and not so much about what God thinks?