Similarly justice needs to be coöperatively defined. A justice that looks merely to existing status will not give lasting peace. Peoples change in needs as truly as they differ in needs. But no people can be trusted to judge its own needs any more than to judge its own right. A justice which adheres rigidly to vested interests, and a justice which is based on expanding interests, are likely to be deadlocked unless a constructive spirit is brought to bear. Abstract rights to the soil, to trade, to expansion, must be subordinate to the supreme question: How can peoples live together and help instead of destroy? This can be approached only from an international point of view. The second obstacle, unsocial competition, is for trade what dominance is in politics. It prevents that solution for many of the delicate problems of international life which coöperation through trade might otherwise afford. Exchange of goods and services by voluntary trade accomplishes what once seemed attainable only by conquest or slavery. If Germany or Japan or Italy needs iron or coal; if England needs wheat, or if the United States sugar, it is possible, or should be possible, to obtain these without owning the country in which are the mines, grain, and sugar cane. The United States needs Canada's products; it has no desire to own Canada. But in recent years the exchange of products has been subjected to a new influence. National self-interest has been added to private self-interest. This has intensified and called out many of the worst features of antagonism and inequality.