This paper offers an explanation for the rise of radical, social movement activity among youth in the United States in the 1960s and for the decline of such activity in the 1970s. Mannheim's theory on generations is used to explain this phenomenon. Mannheim argued that the major historical events of an era will profoundly shape the political and social consciousness and perspective of youth reaching maturity in a particular era. Key historical, cultural, and political events of the late 1950s and the early 1960s are shown to have predisposed an influential minority of young people toward social movement activity and later radicalization. The key to the emergence of the radical youth movements in the 1960s was the Civil Rights Movement of the 1950s and early 1960s, which shattered the political apathy of the 1950s. It was the most important factor in creating and increasing awareness by some young people of the inequalities in American society. Ultimately, this lead to the creation of a sense of injustice about other aspects of American society and a belief that these should be changed by individual and collective action. In contrast, youth who came of age in the later part of the 1960s and 1970s were not involved in social movement activity. It is argued that historical events during this time influenced the generation coming of age into a political orientation with an emphasis on individual fulfillment and not on participation in movements for social change. Proposals are put forth for methods and approaches to study and understand social movement activity among youth. (Author/JK)