Question: Jeremiah 32:27 and Matthew 19:26 say that God is omnipotent (all-powerful). But Judges 1:19 says that the Lord was unable to help the men of Judah drive out the people from the plains, because they had iron chariots. But, in Joshua 10:12, God makes the sun stand still in the sky so that Joshua can get all his killing done before dark. One would have to ask themselves, "if God can make the sun stand still for Joshua to attain a military victory, why did he not do something as simple as destroy a few iron chariots?
Response: The "contradiction," here, is based on two faulty assumptions:
1. That if God was with Judah, then Judah was supposed to win the battle.
2. That the "he" in Judges 1:19, in some of the older English translations, such as the KJV, refers to God rather than to Judah, which was a region in the southern part of the land of Israel.
The newer English translations of the Bible, such as the NIV, make it clearer, for modern English speakers, that the pronoun in Judges 1:19 refers to the people of Judah, rather than to God:
The LORD was with the men of Judah. They took possession of the hill country, but they were unable to drive the people from the plains, because they had iron chariots. - Judges 1:19 NIV.
As for the battle itself, there is no promise in the Bible that the Jews would win every battle. For any number of reasons, the Lord allowed the people of Judah only a limited success at that time and they were unable to conquer the people of the plain. A few possible reasons for this could include:
1). Exodus 23:29 indicates that the Lord would not allow the Israelites to conquer the land of Israel too quickly, because the Jews did not yet have a large enough population to occupy and maintain the whole land.
2). Another possible reason could be that the men of Judah allowed their fear to overcome their faith in the Lord. In fact, in Joshua 17:14-18, we see that Joshua is trying to convince his people that they can overcome troops that have iron chariots. In other words, Joshua 17:14-18 is showing us that indeed there was some fear and doubt among the Israelites as to whether they could defeat iron chariots. (Otherwise, Joshua would not have needed to try to convince them that they could).
3). We see in Deuteronomy 20:1 that the Israelites were not supposed to fear their opposing armies, but to have faith in the Lord instead: "When thou goest forth to battle against thine enemies, and seest horses, and chariots, [and] a people more than thou, thou shalt not be afraid of them; for Jehovah thy God is with thee, who brought thee up out of the land of Egypt."
Another point to remember is that there is a difference between losing a battle and winning a war. For example, the Lord was with Joseph. But Joseph was sold into slavery. But the Lord later used this "defeat" to save Joseph's brothers. The Lord was certainly with Jesus. But Jesus was crucified. And that might have seemed like a defeat, initially, but instead it was the greatest victory of all time. According to Judges 1:19, the Lord was with the men of Judah. But that doesn't mean that they would immediately defeat the men of the plain with the iron chariots.
And one more point to remember: If there is an all-powerful God, then he also would have the power to decide when and how and where to use that power. There is no contradiction there. And there is no contradiction in Judges 1:19.
Source:
http://www.aboutbibleprophecy.com/q16.htm 
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