Judges 3:1-2, 4-6

Now these are the nations that the LORD left, to test Israel by them, that is, all in Israel who had not experienced all the wars in Canaan. It was only in order that the generations of the people of Israel might know war, to teach war to those who had not known it before.

They were for the testing of Israel, to know whether Israel would obey the commandments of the LORD, which he commanded their fathers by the hand of Moses. So the people of Israel lived among the Canaanites, the Hittites, the Amorites, the Perizzites, the Hivites, and the Jebusites. And their daughters they took to themselves for wives, and their own daughters they gave to their sons, and they served their gods.