To go to war for an idea, if the war is aggressive, not defensive, is as criminal as to go to war for territory or revenue; for it is as little justifiable to force our ideas on other people, as to compel them to submit to our will in any other respect. But there assuredly are cases in which it is allowable to go to war, without having been ourselves attacked, or threatened with attack; and it is very important that nations should make up their minds in time, as to what these cases are... To suppose that the same international customs, and the same rules of international morality, can obtain between one civilized nation and another, and between civilized nations and barbarians, is a grave error...