Judges 3:1-2, 4-6

Now these are the nations which the LORD left, that He might test Israel by them, that is, all who had not known any of the wars in Canaan (this was only so that the generations of the children of Israel might be taught to know war, at least those who had not formerly known it)

And they were left, that He might test Israel by them, to know whether they would obey the commandments of the LORD, which He had commanded their fathers by the hand of Moses. Thus the children of Israel dwelt among the Canaanites, the Hittites, the Amorites, the Perizzites, the Hivites, and the Jebusites. And they took their daughters to be their wives, and gave their daughters to their sons; and they served their gods.