Montesquieu

The life of sta­tes is like that of men. Men have a right to kill in the case of natu­ral defense ; sta­tes have a right to wage war for their own pre­ser­va­tion.

In the case of natu­ral defense, I have a right to kill because my life is mine, as the life of my atta­cker is his ; in the same way, a state wages war because its pre­ser­va­tion is just as is every other pre­ser­va­tion.

Among citi­zens, the right of natu­ral defense does not carry with it the neces­sity of attack. Instead of atta­cking, they have only to peti­tion the courts. Therefore they can exer­cise the right of this defense only in momen­tary cases where it would be fatal to await res­cue by the laws. But among socie­ties the right of natu­ral defense some­ti­mes car­ries with it the neces­sity of attack, when one peo­ple sees that a lon­ger peace would put ano­ther in a posi­tion to des­troy it, and that atta­cking is at that moment the only way to pre­vent that des­truc­tion.

Whence it fol­lows that small socie­ties more often have the right to wage war than large ones, because they are more often in the posi­tion of fea­ring they will be des­troyed.

The right of war the­re­fore deri­ves from neces­sity and strict jus­tice. If those who direct the cons­cience or the coun­cils of prin­ces do not limit them­sel­ves to that, all is lost ; and when they base them­sel­ves on arbi­trary prin­ci­ples of glory, pro­priety, or uti­lity, rivers of blood will inun­date the earth.

Above all, let not the prince’s glory be invo­ked : his glory would be his pride ; it is a pas­sion and not a legi­ti­mate right.

It is true that the repu­ta­tion of his might could increase the for­ces of his state ; but the repu­ta­tion of his jus­tice would increase them just as much.