What are three reasons for the rise of conservatism in the late 20th century?

There are a number of reasons for the rise of conservatism in the late 20th century. First, the threat of communism caused many Americans to begin defining themselves and their beliefs in opposition to those of the communists. Part of this included looking to the past (hence the term "conserve") for inspiration and ideas. They celebrated the American founding fathers and the traditions they instituted because these separated them from the communists.

Second, the end of the New Deal era led Americans to seek a new vision for the future. For many Americans, that new vision was conservatism. 

Third, the conservative movement produced charismatic leaders who succeeded at communicating conservative ideals to the American public. Russel Kirk's The Conservative Mind and William F. Buckley's creation of National Review provided the conservative movement with intellectual capital, and politicians such as Ronald Reagan gave conservatives a political outlet.