There was not a town that made peace with the Israelites, except the Hivites, the inhabitants of Gibeon; all were taken in battle. For it was the Lord’s doing to harden their hearts so that they would come against Israel in battle, in order that they might be utterly destroyed, and might receive no mercy, but be exterminated, just as the Lord had commanded Moses. – Joshua 11:19-20 
 
Reading the phrase the Lord hardened their hearts, we have to wonder, does God harden the hearts of people so that they sin? So why did God harden their hearts? If you look at verse 19, it says, Not a town made peace with the Israelites except the Hivites. It means God was expecting them to change and make peace with Israel, but they did not. The word hardened means to strengthen. God did not cause them to sin; they already sinned and chose to remain in their sins, so God strengthened their stand, not forcing them to do what God wanted until they fell into God’s judgment. This story reminds us that God will not interfere with our free will if we choose to sin. He wants us to choose freely to forsake sin, come to Him and make peace with Him. Decide to make peace with God and ask for forgiveness, and He will forgive you and cleanse you (1 John 1:9)