Judges 3:2 explains He did this only to teach warfare to the descendants of the Israelites who had not had previous battle experience.  God left people in the promised land for the Israelites to remove by force.

It seems like God would simply send a plague to these inhabitants then Israel could just easily walk into the promised land and occupy it as their new country. Instead, God made Israel strap on a sword, grab a shield and go daily into battle if they were going to realize His promise for them.

Why did God do this? (more…)