‘ And the children of Israel cried to Yahweh, for he had nine hundred chariots of iron, and he mightily oppressed the children of Israel for twenty years.'
They once again recognised that Yahweh alone could help them in a situation like this and began to turn from their idols and to seek Him once again, paying more attention to the tribal covenant, becoming more faithful to the central sanctuary, and reinstating the law of God. The old ways had never been completely forgotten, but had fallen into partial disuse. Now they were restored.
“For he had nine hundred chariots of iron.” Gathering together the strength of his confederate cities he possessed nine military units (‘hundreds') of chariots. No wonder they cried to Yahweh. Who else could deal with a menace like this? The nine may represent a threefold three, thus signifying totally complete in itself.
“And he mightily oppressed the children of Israel for twenty years.” This was longer than both Cushan-rishathaim and the Moabites, although the latter in a totally different area and possibly concurrent. ‘Mightily oppressed' suggests that this was worse than they had previously experienced anywhere among the tribes, partly possibly in consequence of revenge because of the ruin that they had previously brought on Hazor, and their behaviour then. They had not been too kind either. The tribes in mind here would include Naphtali, Issachar, and Zebulun and possibly parts of Manasseh. They were thus impoverished and ill-used.
Eight (Judges 3:8), eighteen (Judges 3:14), twenty (Judges 4:3) years of oppression might not seem to us a progression mathematically, but it would be different to his readers. For eight progressed to eight plus ten and then to doubled ten. They were increasing in intensity.