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 established by one system of law.' It is this capacity of contributing to a common good that tests the development of the relations between States. According as the organization of these relations becomes more nearly complete, 'the more the motives and occasions of international conflict tend to disappear, while the bonds of unity become stronger'.

The place of International Law, said Henry Sidgwick, is intermediate between Positive Law and Positive Morality, and parts of it 'have reached a degree of definiteness that makes it resemble the former more than the latter. But this is not the case with the most important rules of international duty'. International duty is not to be determined on the basis of exclusive regard for 'national interest', and where the two conflict the former must be held paramount. Generally, however, 'though not always', it is the interest of a State 'to observe the recognised rules of international duty, so long as it has a reasonable expectation that they will be observed by other States. It is a more doubtful question whether a State ought to risk war to prevent high-handed aggression by another State against a third.'

If we examine the lawfulness of war by right reason, said Grotius, and by the nature of human society, which is the second and most nearly perfect rule to judge by, we shall plainly perceive that it is not all manner of force that is thereby forbidden, but that only which is repugnant to human society—that, namely, which invades the right of another.