Part of the restoration of the people of Israel (and Judah and Jerusalem) is the judgment from God upon those nations who took advantage of the people of Israel when they were down, either by warring against them, or taking advantage of them in their time of poverty and taking the people into captivity. Just as God restores His people after this time of difficulty, He will also seek revenge on those who took advantage of His chosen people.
A couple of things concerning this revenge: first of all, vengeance belongs to God, and not to people. He has the power and the ability to repay them for all that they had done. Second, sometimes He uses people or nations to do that. Notice verse 10 (a reversal from a famous passage Isaiah 2:4), God is raising up His warriors to be His instruments of justice. Yet it is still God who judges.
Often in our lives, we try to take revenge into our own hands. Yet our revenge is sinful, no better than those who hurt us. The vengeance belongs to the LORD, and that day of judgment of the wicked will be viewed as that horrible day of the Lord, yet to God’s chosen people, those of us who believe in Him, He will be our refuge on that day!