An animated historical documentary from our friends at Kings and Generals describing the early progression involved in Japan's adoption of Buddhism.
Take notice of the political involvement in the spread, propagation, and institution building surrounding Buddhist propagation in Japan throughout history. Also, consider how Buddhism, Taoism, and Confucianism intermingled with nativist Shinto to develop into a unique syncretism that influenced Japanese culture.
Since Buddhist organizations were dependent upon political patronage from the very beginning, it should come as no surprise that the major institutions supported Imperial Japan's aggressive wars, leading into World War II, as detailed by Christorpher Daizen Victoria's great book: Zen at War.