You might have conflated the Millenial Kingdom with the Eschaton (i.e. new heavens and new earth). In the millennial kingdom, the tribulation saints will reign with Christ, regardless of nationality or ethnicity; in the eschaton, ALL nations, as one Body of Christ without distinction, walk on the golden street bathed in the light of the Lamb.
And I saw thrones, and they sat on them, and judgment was committed to them. Then I saw the souls of those who had been beheaded for their witness to Jesus and for the word of God, who had not worshiped the beast or his image, and had not received his mark on their foreheads or on their hands. And they lived and reigned with Christ for a thousand years. (Rev. 20:4)
Each one’s work will become clear; for the Day will declare it, because it will be revealed by fire; and the fire will test each one’s work, of what sort it is. If anyone’s work which he has built on it endures, he will receive a reward. If anyone’s work is burned, he will suffer loss; but he himself will be saved, yet so as through fire. (1 Cor. 3:13-15)