Judges 3:1-2, 4-6

Now these are the nations which the LORD left, to test Israel by them (that is, all who had not experienced any of the wars of Canaan; only in order that the generations of the sons of Israel might be taught war, those who had not experienced it formerly).

They were for testing Israel, to find out if they would obey the commandments of the LORD, which He had commanded their fathers through Moses. The sons of Israel lived among the Canaanites, the Hittites, the Amorites, the Perizzites, the Hivites, and the Jebusites; and they took their daughters for themselves as wives, and gave their own daughters to their sons, and served their gods.