Chariots of iron were not made entirely of iron but wood with iron reinforcement.1 They would be particularly effective on level ground but not in the hills. These chariots are mentioned as a reason for why the people of Joseph could not drive out the Canaanites. This reason has, however, already been shown to be false (see Joshua 11:9). With the Lord helping them, they could have driven the Canaanites from the land. They had the power to remove them and serve as God’s instruments of war but preferred the peace that comes from tolerating wickedness to war for righteousness.2
16 The people of Joseph said, “The hill country is not enough for us. Yet all the Canaanites who dwell in the plain have chariots of iron, both those in Beth-shean and its villages and those in the Valley of Jezreel.”