“The Constantinian Imperial churches condemned early Christian millennarianism because they saw themselves in the Christian imperium as “the holy rule” of Christ’s Thousand Year empire. So every future hope for a different, alternative kingdom of Christ was feared and condemned as a heresy” (Moltmann, xv).
I am not making the claim that a Christendom-model is necessarily bad. I just find it interesting that condemnations of chiliasm by the church happened around the same time that the Imperium became officially Christian. I need to reread Oliver O’Donovan’s Desire of the Nations and see if he specifically interacts with this point.