Young people in their teens and early twenties stand, usually hesitant, on the threshold of life. They are bursting with energy, eager, hopeful, anxious to enter the stream of adult activity. Inexperienced, they under-estimate the difficulties, taking up any line of activity that promises quick results. They are impressionable and generally seeking "a good life." Such resources of energy and idealism exist in every generation and reappear as the generations follow one another. Youth groups have played active roles in one country after another where opportunities were restricted by the establishment and revolutionary propagandists painted a rosy future. Political nationalism in the eighteenth century and economic and social emancipation in the nineteenth century mobilized high school and college age youth in the Americas, Europe, Asia and Africa. It is folly to assert that human nature is a given and unalterable quantity in every social situation and that since "you cannot change human nature" intentional social changes are out of the question. The facts are otherwise: 1. There is a wide diversity in human beings ranging from herculean physical strength to pitiable weakness; from the mental power of genius to the nonentity of imbecility; from outstanding and unquestionable talent in arts and letters to illiteracy and clumsy inefficiency. This wide diversity in human capacity is one of the outstanding features of human nature, recorded again and again in history and encountered in all human aggregates. 2. There is a period in human life when the habit patterns of childhood are exchanged for the habit patterns of adulthood. At this turning point, youth is likely to follow dynamic and purposeful leadership. 3. There is a wide diversity in social situations, from rock-ribbed stability, to entire communities teetering on the brink or plunging over the brink into the maelstrom of revolution. Such diverse situations have existed again and again during the 1750-1970 revolutionary epoch. 4. When a revolutionary situation develops, a revolutionary leader well-established in a community trembling on the brink of a revolutionary overturn may seize the reins of power and establish a regime founded on opposition principles, dedicated to another set of principles and practices. When such a revolutionary coup is successful the bells of history have tolled for the older order and the trumpets of victory have sounded for the new society. 5. The intensity and the direction of the social changes which radiate out from the climax of a revolutionary situation and the consequent, subsequent attempts at counter-revolution, are the outcome of active, purposive intervention by all of the social groups present at the center of revolutionary activity.