So it would have taken some kind of miracle for them to win, is what you're saying.
Not what I am saying...
Isaiah 55:8
For my thoughts are not your thoughts,
neither are your ways my ways,
declares the Lord.
It says God was with the men of Judah. Therefore, what happened was God's will. They actually did God's will, even if they wanted personally to do otherwise. God's ways were not that of the desires of men. Surely the Jews wanted to win. But, once they sensed God was not in it, they backed down and accepted God's will. For they knew if God wanted the Jews to be victorious, it would have been theirs to have.
Now...If we took it your way of thinking and applied it to Israel? Then, Israel should have conquered the entire world! But, God did not want all the world to be His. Only his select people were to be His own possession at that time. The world was Satan's kingdom, and God recognized that.
God knows what works best in revealing his righteousness when there is something to contrast with. At his fall Satan wanted to replace God. Satan thought He was even better than the Lord. By having one small nation dedicated to God's Law, God wanted to show Satan what a low life he really was by setting up a small nation of his own, to contrast with barbarism and brutality that Satan's fingerprints were written on all over in the pagan nations around Israel.
Its one reason why the Jews looked down on the Gentiles as trash in that day. God had to warn the Jews against bestiality and incest because such practices were not taboo in the pagan nations around them.
That also included the prohibition against child sacrifice. Satan's world was depraved and primitive. God shined a powerful light upon that darkness by the light God caused Israel to become. That light was the light of the world during the times the Jews were being faithful to God's Law.
At other times, the Jews slipped into degeneracy as they imitated the ways of Satan's system. That is why God punished Israel so severely at certain times. God dispersed Israel and sent them into captivity several times as to chastise them. Its one reason why they had three temples in Jerusalem, not just one. For each one got destroyed when God brought the hammer down on an arrogant and disobedient Israel.