Kant does not directly present political republicanism as apocalyptic, but his idea of republicanism is intertwined with theological ideas about the direction of history, which as Kant himself notes even as he develops a rationalistic view of religion, includes some idea of a termination of history as God appears in it, what Christianity refers to as the Second Coming.
The Conflict of the Faculties follows up a discussion of the limits of moral terrorism, eudaemonism, and abderitism, as ways of understanding the direction of human history, with an account of the international reaction to the French Revolution as one of sympathy and the wish for participation. This provides reason to think that history has a eudaemonistic purpose, which Kant suggest must mean a chiliastic end, that is a religious apocalyptic end.
This eudaemonistic prophetic history is of the spread of republican constitutions, as in France, the only kind of constitution which recognises legislation by a people according to public use of reason. The justification we have for thinking that the future is republican is the universality of sympathy for the French Revolution, though that Revolution contains violence and chaos which nobody should want to repeat.
The republican orientation of humanity contains then a risk of the recurrence of violence, even if that is not the desired outcome, so we have to take Kant as at least considering the possibility that the republican future will come about through an increasing number of violent revolutions, undesirable though that violence may be. One reason for hoping for a republican future in Kant’s account is the expectation that republics will not go to war with each other, but it is clear that moving towards republicanism increases the possibility of war in the struggle for a republic.
Kant’s own account of peace and republicanism is ambivalent. He both brings up the possibility of universal peace in a world of republics and argues for the impossibility of the realisation of that goal. Perpetual peace is the peace of the graveyard as where there is life there is the possibility of the use of violence, so nothing can guarantee the end of war even if a world of republics creates the best possible conditions for peace.
Kant at some points even suggests that war is a desirable part of human society, as when in his account of the sublime he suggests something elevating about war fought according to respect for law, and something lacking in human societies unwilling to enter into the sublime experience of war. One way of thinking about how this might be resolved in Kant is that a world of republics would be a world moving towards the violence of the divinely inspired end of history. There is no direct suggestion of such a thing, but Conflict of the Faculties gives reasons for looking at political history in a way which is prophetic, eudaemonistic, and chiliastic.
The account of a church operating according to reason, and therefore as a church should operate in a republic, in Religion within the Boundaries of Mere Reason, has its own prophetic chiliastic orientation, which takes the Reformation as step towards the apocalypse. In the pre-Reformation world, the identification of church leadership with political power was itself responsible for religious violence and war, including the Crusades against Islam.
Protestantism separates the church from the state, so making external power structures progressively less necessary in the church itself. That is once Christianity is understood as inner experience rather than the following of externally imposed laws, the whole role of church government declines. We seem to be moving even beyond political republicanism to an inspired community beyond laws imposed by the state, or any external force. Arrival at that situation is for Kant the arrival at the time when the Apocalypse is very close.
The separation between church and state argued for here can be found in a monarchy, but it is clear that is in a republic that there is the greater affinity between political institutions and the power of the invisible church. Monarchy has distinct tendencies towards tyranny for Kant, except in so far as the monarch is constrained by republican institutions which put law making in the hands of the representatives of the people, or in so far as the monarch chooses to behave as if that was the case. However, even the republic itself does not match the perfect equality between believers of the invisible church.
In The Metaphysics of Morals, Kant distinguishes between active and passive citizens, which is a distinction based on differences in economic status. The individual employed by another individual does not have the independence necessary to vote or become a representatives, which are both reserved to the economically independent active citizens. The state needs separation from religion to develop legislation according to popular will, but it is the church where complete equality between citizens is possible, so it is only there that pure ‘republicanism’ can appear.
The most advanced republicanism is a situation where the church has developed so far in its egalitarian and inner mission that all political institutions are soon to be eliminated in a Chiliastic destruction which will put to an end dilemmas about war. In ‘What is Enlightenment?’, Kant singles out religion as what will be most transformed by the autonomous use of reason. The religious transformation accompanies greater public participation in debates about laws, but the Enlightened discussion of laws is speeding up the theological end of history and any need for republican aspects to politics as well as Enlightenment itself. Evaluation of Kant’s republicanism needs to take this self-terminating apocalyptic aspect into account as well as the aspect of providing normative foundations for the best kind of state.