National group self-consciousness plays, then, an all-important part in the life of nations, is in fact the actual, the most essential constitutive factor of every nation; and nationhood or the principal of nationality is the dominant note of world history in the present epoch; that is to say, the desire and aspiration to achieve nationhood, or to strengthen and advance the life of the nation, is the most powerful motive underlying the collective actions of almost all civilised and even of semi-civilised mankind; and the consequent rivalry between nations overshadows every other feature of modern world history, and is convulsing and threatening to destroy the whole of modern civilisation. It is surely well worthy of serious study. Yet, owing to the backward and neglected state of psychology, not only is this study neglected, but, as we have seen, some of our leading political philosophers have not yet even realized the essential nature of the problem; and many of the historians, economists and political writers are even further from a grasp of its nature. They have been forced by the prominence and urgency of the facts to recognise what they call the principle of nationality; and even now the majority of them are demanding that, in the European settlement and in the affairs of the world in general, the principle of nationality shall be given the leading place and the decisive voice. But they do not recognise that the understanding of this principle, this all-powerful political factor, is primarily and purely a psychological problem. We find them, in discussing the nature of nations and the conditions of nationality, perhaps mentioning the psychological view of nations as a curious aberration of a few academic cranks, from which they turn to discover the true secret of nationality in such considerations as geographical boundaries, race, language, history, and above all economic factors; they do not see that each and all of these conditions, real and important though they are and have been in shaping the history and determining the existence of nations, only play their parts indirectly by affecting men's minds, their beliefs, opinions, and sentiments, especially by favouring or repressing the development in each people of the idea of the nation.