From Amill Objections to Psalm 2 Use by Kenneth L. Gentry:
Amillennialists often object to postmillennialism’s use of this verse [Psalm 2:8]. They complain that postmillennialists apply the terms ‘nations’ and ‘earth’ in a way that Jesus and the apostles never intended: as political entities. The amillennialist argues that the NT teaches that Christ’s making the nations and the earth his footstool simply refers to the salvation of scattered Gentiles from every tribe tongue and nation, not Christ’s influence on political structures, etc.
Second, I don’t see the problem with using Psalm 2:8 as evidence of postmillennialism. […] He is not speaking merely of scattered converts here-and-there from out of the nations. Rather he seems clearly to be speaking of vast influence over all the nations and even to the very ends of the earth. The psalm appears to be speaking of some sort of global dominance.
Third, nevertheless, I would note that David does call upon the kings and judges of the earth to do homage to the Son (Psa 2:10-12). It seems he goes to great lengths to speak of not only people in general but even their political rulers and judges.
Some people — especially the political power elite, but also their their religious go-fers and mouthpieces — would be a lot happier if God would just stay in the tiny little box assigned to Him in some church or shrine or temple somewhere, and leave serious men alone to do, to say, and to rule as they please.
God explicitly will not do this, as spelled out clearly in the Psalms.
Especially Psalm 2.
That wineskin is going to burst wide open. Regardless of the will of the clergy.
Or the political powers, backing the clergy on this matter.
Or that spiritual power, backing the politicians on this matter.