The Zen sect of Buddhism has long been associated with the bushi. D. T. Suzuki and many others have gone on at length about how Zen discipline was a perfect match for the austere, violent life of Japan's warrior class.
At the same time, Zen was, in its introduction to Japan, a fundamentalist sect. A number of Buddhist sects, like Tendai and Shingon, had become very intellectualized and practiced various forms of what we would call magic (mikkyo - "secret teachings"). Meditation played only a limited part in their religious practices. The Zen monks wanted to get back to the fundamentals of their religion: emphasis on meditation as the route to enlightenment.
For some reason, in the '60s, Zen became popular among some Western intellectuals. This really makes no sense on the face of it. Why would Western professors and artists study Zen, the sect of brutal feudal warriors, a fundamentalist sect that was essentially anti-intellectual? Maybe they saw it as anti-authority, since it was an assault on the established, and politicized, Buddhist sects of the day. How far you take that depends on how much history you are willing to ignore, of course.
It's just my experience, but most non-Asian Buddhists seem to be trying to replace Christianity and Western culture. They are willing to ignore a great deal in order to displace their native culture, which they consider corrupt and, often, basically evil. You can see this when they talk up their chosen faith to prove it's superior, and because they are also very critical of and condescending towards Christianity.
The point for them isn't that they have found Buddhism, but rather that they have rejected Christianity, often the West, and specifically America. It is the rejection and unfavorable comparison that is important, and their "evangelism" is to show up the average Christian, and the average Westerner, and say "ha-ha, look what I've found, you ignorant wretch."
I think this is true of many Westerners who have joined Eastern or non-Christian religions. Certainly not all of them, but I've found this true of many of the people I've known who were involved in New Age practices. Also, I personally think the Nation of Islam sect was founded on this emotion.
Living in Japan, I've found the most vocal anti-Americans are some of the American ex-pats, as if the more they despise their own country the more they will be accepted in their chosen society. The next loudest group consists of most ex-pats from other nations, who, while not as loud about it, seem to feel it deeper.
The Japanese, while they have complaints, on the whole seem to like America. Certainly the Zen monk I hung out with for a year did.