The great revolution is changing man's relation to nature, to the structure and function of human society and the ways in which men think, feel, act and live. The great revolution has shifted the human living place from rural to urban, replaced a large measure of self-employment by wagery, lifted large segments of mankind out of scarcity into abundance, led to widespread migrations across Europe and from continent to continent, expanded nations and built empires. In the course of these developments Europe became the center of world economic, political and cultural affairs, held the position briefly and lost it in the course of two general, suicidal wars. Speaking broadly, such a period in the life of any society may be described as a revolutionary situation--one in which changes are made frequently, rapidly and with far reaching consequences. In a word, the existing social pattern is in process of being turned over, turned upside down, transformed by forces which seem to operate according to their own principles and often quite independently of human intention or intervention. Our society--western civilization--is undergoing a revolution. People born into a rapidly changing society are often tempted and sometimes compelled to play significant roles in the revolutionary process. Unconsciously or consciously, unwilling and unwitting or deliberately and purposefully they are revolutionaries. Among the participants in the revolutionary process, the far-seeing, imaginative, perceptive and mature develop into purposive revolutionaries. In the course of a series of political, economic and cultural revolutions like those which played so fateful a part in China between 1899 and 1969, an entire generation is born, grows up and, in larger part, retires from active life or dies off. Long continued cultural changes play a part in local history. They have an equally important role in the lives of neighboring nations and peoples. With present means of communication, transportation and travel, the influence of revolutionary events such as those in China from 1899 to the present day may be profound. The bourgeois revolution from 1750 to 1840 centered largely in West Europe and the Americas. In scope it was economic, political, cultural. The Chinese and other revolutions of the present period, beginning with the Mexican Revolution of 1910 and the Chinese Revolution of 1911, are once more transforming the economic, political and cultural life of mankind. UNESCO's _History of Mankind_ (Harper and Row), particularly its Volume 6 titled _The Twentieth Century_, presents voluminous comments from a wide range of qualified scientists and commentators on the changes associated with the great revolution of 1750-1970.