It was of the Lord to harden their hearts... that he might destroy them. — Or rather to strengthen their heart — i.e., render them obstinate. These words go to prove what has been said elsewhere, that the conquest of Canaan was not intended to be a massacre of the unresisting inhabitants.
Related Commentaries of Joshua 11:20
Joshua 11:20
20 For it was of the LORD to harden their hearts, that they should come against Israel in battle, that he might destroy them utterly, and that they might have no favour, but that he might destroy them, as the LORD commanded Moses.