All wars are accordingly so many attempts (not in the intention of man, but in the intention of Nature) to establish new relations among states, and … - Immanuel Kant

It is not without cause that men feel the burden of their existence, though they are themselves the cause of those burdens.

The master is himself an animal, and needs a master. Let him begin it as he will, it is not to be seen how he can procure a magistracy which can maintain public justice and which is itself just, whether it be a single person or a group of several elected persons. For each of them will always abuse his freedom if he has none above him to exercise force in accord with the laws. The highest master should be just in himself, and yet a man. This task is therefore the hardest of all; indeed, its complete solution is impossible, for from such crooked wood as man is made of, nothing perfectly straight can be built. That it is the last problem to be solved follows also from this: it requires that there be a correct conception of a possible constitution, great experience gained in many paths of life, and — far beyond these — a good will ready to accept such a constitution. Three such things are very hard, and if they are ever to be found together, it will be very late and after many vain attempts.

I do not say that things in themselves possess a quantity, that their reality possesses a degree, their existence a connection of accidents in a substance, etc. This nobody can prove, because such a synthetic connection from mere concepts, without any reference to sensuous intuition on the one side or connection of such intuition in a possible experience on the other, is absolutely impossible.