This point is amplified by consideration of what kind of person is required for a republican constitution to exist. In response to those (such as Robespierre?) who think that it would require angels for such a state to exist so that a republic is indistinguishable from a state of virtue, Kant argues the reverse. The basic self-seeking inclinations of human beings is sufficient in itself to point to the need for states to exist. In arguing this Kant points out that the question of how to regulate such self-seeking requires organisation so that the interest of one clashes with the interest of another in such a way that they cancel out. The result of this is that the behaviour of the people in question will emerge as of a sort that would be equivalent to the self-seeking inclinations not even existing.
So rather than a republic being a state of virtue it is plausible even for devils to come together in such a condition. The problem of state formation is not equivalent to one of moral improvement since all that is required is, as Kant puts it, using "the mechanism of nature" (Ak. 8: 366). The mechanism at issue appears to me to be the one of forces of attraction and repulsion producing states of equilibrium. (Directly referred to in the Doctrine of Right: Ak. 6: 232.)
Setting forces of self-seeking into such states of equilibrium does not require that self-seeking is itself abolished, only that it is regulated. Any state that exists will have this in view as a key part of its mission despite the fact that states are generally imperfect and do not meet the conditions of the republican constitution. The moral improvement of the people will thus emerge in a sense as a result of the republican constitution but not due to the constitution being based on moral requirements. Hence reason can use the mechanism of nature as a means to promote the rule of right as this mechanism will, if regulated to create mutual checking of inclinations, promote this in an automatic sense.
This argument shows one basis of Kant's view that there is a "guarantee" of perpetual peace in nature and establishes the ground for the existence of states in general not on any historical commitment to social contracts but instead on two requirements that are not in themselves moral. Firstly, the need for security of any people in an area forcing organisation upon them to resist the rapine of others. Second, the self-checking of inclinations when regulated together in a state framework. This hence provides the first illustration of Kant's general argument for a "cunning of nature".