Jeremiah 49:28-33. Jeremiah's prophesying against all of the lands surrounding Judah - they are all in for a fall. Here he speaks to Kedar and Hazor, which the king of Babylon has smote. The Lord says "Rise up, advance against Kedar! Destroy the people of the east!" Everythin shall be destroyed or taken. Men shall cry "Terror on every side!" because Nebuchadnezzar has made a plan against them. They are at ease, dwelling securely, but God "will bring their calamity from every side of them."

When things got so bad in Judah that the Lord had to allow Babylon to destroy it, the evil was not just confined to his chosen people. All the nations and people surrounding Judah were acting just as badly. In fact, it was the corruption of those people, and the failure of the Jewish priests and leaders to stop that corruption from coming into Judah, that made God's people as bad as they were. Everyone was behaving so terribly, the priests and leaders included, that the everyday Jew just got swallowed up in the evil. They had free will, don't get me wrong, but they were also exposed to tremendous evil presented as good or tolerable and they had no one to teach them the truth, (other than prophets like Jeremiah)!

So while God allowed for the complete destruction of Judah by Babylon, and the exile of his people, in order for them to learn to turn back to Him, He was not going to leave the surrounding lands unpunished. He says in Jeremiah 49:12 "If those who do not deserve to drink the cup must drink it, will you go unpunished?" If his misled people had to be conquered and exiled, then God's wrath will also be felt by the nations that had corrupted them.

This makes sense even from a realistic point of view. In order to raise up a force great enough to utterly destroy Judah, God had to allow that force, the king of Babylon, to become mighty indeed (not that he would not fall later). When any person on earth who is not properly oriented towards God becomes so powerful, there is no way that he will stop at just acquiring one kingdom or one victory. Power corrupts, it makes powerful people seek more and more victories.

Thus, God knew what He was doing in allowing Nebuchadnezzar to become as powerful as he did. The king of Babylon accomplished all of the smiting that God is promising in these chapters of Jeremiah, before meeting his own ignoble end later.