Deuteronomy 7:2

and when the Lord, thy God, shall deliver them before thee, give them into the hands of the children of Israel, so that they would be witnesses of His power, thou shalt smite them and utterly destroy them, it was to be a war of extermination, Thou shalt make no covenant with them, nor show mercy unto them, give them no quarter, reject all offers of submission. The measure of sins of these heathen nations was full, and therefore the Lord wanted them to he removed entirely.