John Wesley on Joshua 11:20

To harden their hearts - It was the design of God's providence not to soften their hearts to a compliance with the Israelites, but to give them up to their own animosity, pride, confidence and stubbornness; that so their abominable and incorrigible wickedness might be punished, and that the Israelites might not be mixed with them, but be entire among themselves in the possession of the land.