In Japan the connexion between numerical increase and a possible war is now coming to be recognized here. Australia, New Zealand and the United States are already definitely conscious of it. The Japanese religion, based upon piety towards ancestors (to whom every man is bound to perpetuate his family), and upon loyalty to the Mikado who, as Emperor God, is held to be divine, imposes upon all faithful subjects the duty of marrying young and of producing many children. This injunction is again promulgated irrespective of the native resources of Japan, and in the past has necessitated a considerable annual emigration to other countries. The recent restrictions imposed by America upon Japanese immigration, themselves prompted by motives common to most English-speaking races, have led directly and inevitably to the existing tension between America and Japan. As things stand at present, it appears that this tension is likely to increase and may easily eventuate in a war, in which there would be a greater probability of our being involved than there was, initially, of America being involved in the late war. Both the Americans and Japanese are sensitive and proud people. After further tension has accumulated, a trivial incident――the possible murder of an American official in Japan by some irresponsible person――might lead to the despatch of a curtly-worded note or to the formulation of an abrupt ultimatum out of which a second world war might, like the last, suddenly flare up, to reduce modern civilization to ruins and ashes. Stress is laid on this particular aspect of the population problem partly because it is felt that few nations now hold the desirable ideal of adapting their numbers to their particular economic optimum, and partly because it would seem that in face of this nationally encouraged increase of population and of certain apparently unalterable race antipathies, _no amount_ of international pacifism, or of condemnation of violence, or of genuine humanitarian goodwill can prevent war. Germany and Japan display the connexion between numerical increase and wars most clearly to-day. It is possible that in the future other nations may become conspicuous in this respect. Thus America, where the teaching of contraception is illegal (in so far as anything is), may, in another 50 or 100 years, develop an aggressive foreign policy. And now that restrictions have been imposed on the entry of Italians into America, it is conceivable that Italy may at some time discover an Imperialist mission on the shores of the Mediterranean. (_b_) _Social._――This aspect of Birth Control has been much discussed and is concerned with the dimensions and quality of the population of these islands. The argument, in the form in which it is usually advanced, distinguishes a quantitative and a qualitative point of view, the latter further possessing two aspects.