Albert Barnes Commentary Judges 3:1

"Now these are the nations which Jehovah left, to prove Israel by them, even as many [of Israel] as had not known all the wars of Canaan;" — Judges 3:1 (ASV)

Even as many of Israel ... - These words show that the writer has especially in view the generation that reached adulthood immediately after the close of the wars with the Canaanites (Joshua 23:1). Compare (Judges 2:10).