This is Kant's answer to Rousseau.
The full realisation of man's rational nature is possible only in a "universal civil society" founded on political justice.

The establishment of such a society is the highest problem for the human species.

Kant contemplates, as the political goal, a confederation of states in which the utmost possible freedom shall be united with the most rigorous determination of the boundaries of freedom.
Is it reasonable to suppose that a universal or cosmopolitical society of this kind will come into being; and if so, how will it be brought about?
Political changes in the relations of states are generally produced by war.

Wars are tentative endeavours to bring about new relations and to form new political bodies.

Are combinations and recombinations to continue until by pure chance some rational self-supporting system emerges?
Or is it possible that no such condition of society may ever arrive, and that ultimately all progress may be overwhelmed by a hell of evils?
Or, finally, is Nature pursuing her regular course of raising the species by its own spontaneous efforts and developing, in the apparently wild succession of events, man's originally implanted tendencies?
Kant accepts the last alternative on the ground that it is not reasonable to assume a final purpose in particular natural processes and at the same time to assume that there is no final purpose in the whole.
Thus his theory of Progress depends on the hypothesis of final causes.
It follows that to trace the history of mankind is equivalent to unravelling a hidden plan of Nature for accomplishing a perfect civil constitution for a universal society; since a universal society is the sole state in which the tendencies of human nature can be fully developed.