Nowhere in the context of Judges 1:19 say that Judah and his army were afraid of the people in the valley with the iron chariots. Therefor Judah did not do anything wrong. "The Lord" just couldn't deal with superior tech. He's not omnipotent.

The "he", in Judges 1:19 is Judah, not God. Just as they feared the giants in the book of Numbers, they feared those with iron chariots, and just as God didn't help them fight the giant because they lost their faith in God because of their fear, God did not help the Jews because their lost their faith in God through fear. And that is why Judah could not drive out the inhabitants of the mountain.

Well, I'll be Goddammed ...but then again, if I'm lucky, he fails at that too.