Was John Calvin a Postmillennialist?
But it may be objected, Ought we to ask from God what, he declares, will never exist to the end of the world? I reply: When we pray that the earth may become obedient to the will of God, it is not necessary that we should look particularly at every individual. It is enough for us to declare, by such a prayer as this, that we hate and regret whatever we perceive to be contrary to the will of God, and long for its utter destruction, not only that it may be the rule of all our affections, but that we may yield ourselves without remorse, and with all cheerfulness, to its fulfillment.
In other words, just because all the people in the world are never going to obey the will of God we do not have an excuse not to. So we look forward to that great day when Christ will return and overthrow all rebellion, even as we seek his holy war against the sin in us now.