Now, as a matter of fact, the morally practical reason utters within us its
irrevocable veto: There shall be no war. So there ought to be no war, neither
between me and you in the condition of nature, nor between us as members of
states which, although internally in a condition of law, are still externally
in their relation to each other in a condition of lawlessness; for this is
not the way by which any one should prosecute his right. Hence the question
no longer is as to whether perpetual peace is a real thing or not a real
thing, or as to whether we may not be deceiving ourselves when we adopt
the former alternative, but we must act on the supposition of its
being real. We must work for what may perhaps not be realized, and
establish that constitution which yet seems best adapted to bring it
about (mayhap republicanism in all states, together and separately).
And thus we may put an end to the evil of wars, which have been the chief
interest of the internal arrangements of all the states without exception.
And although the realization of this purpose may always remain but a pious
wish, yet we do certainly not deceive ourselves in adopting the maxim of
action that will guide us in working incessantly for it; for it is a duty to
do this.
Immanuel Kant. 1790. The Science of Right.