11:20 harden their hearts. The Lord did not want them to seek peace treaties with Israel, as Gibeon had done, so constrained them to aggressively fight against Israel (Joshua 11:5).
11:20 destroy them utterly. Many skeptics and liberals have charged Joshua (and God) with unnecessary cruelty and bloodthirstiness, for visiting such utter destruction on all these Amorites (or Canaanites). But it should be remembered that they had already had many centuries to repent of their extreme wickedness and cruelty (note Genesis 15:16), and had only grown worse. It was merciful for God to command their destruction before they could (as they would, and did) contaminate others. At least their infants, who had not yet committed these sins, and had not yet rejected the true God as their parents had, would be spared future lives of licentious evil and cruelty by dying young.