Since the World Parliament of Religions in 1893, Buddhism has been a recognized aspect of religious life in the American landscape. Yet before the Beat movement of the 1950s, Buddhism in the United States was largely restricted to the Jodo Shinshu interpretation of Pure Land Buddhism, which in turn was practiced almost exclusively by Japanese immigrants and their descendents. World War II and the consequent internment of Japanese American citizens did little to improve the overall standing of the dharma in America, and led many Jodo Shinshu practitioners to adopt a very Protestant form of worship, complete with churches, pews, hymnals, Sunday school, and the like - all in an attempt to make Buddhism appear less threatening to Americans.
This began to change somewhat with the emergence of the Beat poets, who took a strong liking to the watered down form of Zen presented by D.T. Suzuki. Beat Buddhism was somewhat notorious for its self-absorbed, ill-informed character, but served to lay the groundwork for the Zen explosion of the 1960s counterculture.
What separated 1960s Zen from 1950s Zen was the presence of genuine Japanese Roshis - though it is important to note that these teachers, such as Hakuun Yasutani and Shunryu Suzuki, were often renegades in their own right, who hoped to take what they saw as a degenerating religion in Japan and revitalize it on American soil. This led to the incorporation of certain unorthodox practices as normative for most American converts, such as blending the zazen meditation of the Soto school and the use of koans particular to the Rinzai school far more frequently than was normally practiced in Japan.
Perhaps more important than the flood of converts from the counterculture, however, was the loosening of immigration quotas from non-European countries in 1965. This led to a wave of immigration from Asian countries that has yet to abate, and has subsequently introduced a myriad number of Buddhist traditions - many of which are a direct contradiction of the convert understanding of Buddhism as an atheistic, rational tradition. Tibetan Buddhism, Soka Gakkai, and traditionalist Therevada Buddhism, to name only a few, have become every bit as important to the American Buddhist landscape as their more "rationalist" counterparts in the Zen and Vipassana meditation movements.
This has led those who try to discuss the phenomenon of Buddhism in the United States to often fall into two distinct camps: those who dismiss native Buddhist traditions as superstitious corruptions of the original teachings of the Buddha, and those who dismiss convert Buddhists as practitioners of a watered-down travesty that can't make up their minds as to whether they are monks or laypeople. Not surprisingly, the former camp comprises largely of converts and old-school Western professors of religion, while the latter camp is made up of immigrants, traditionalists, and the newer crop of religion professors along with their counterparts in anthropology.
What both sides often fail to see is that perhaps the development of a lasting form of Buddhism in America will require the input of both immigrants, for their sheer numbers and greater understanding of tradition, and converts, for their necessary adaptations to American culture. The United States has never been a culture that is terribly supportive of monasticism, the key ingredient to the survival and flourishing of Buddhism in other countries. The convert practice of adapting meditation into day to day life, something that had previously been pursued only by monastics, is perhaps the only way for Buddhism to survive in our highly materialistic, worldly culture. On the other hand, the input of traditionalist immigrants may prove necessary to prevent converts from picking and choosing to the point that what they practice is no longer recognizable as Buddhism.