Nichiren's philosophy was partly a reaction to the corrupt and dissolute conditions that characterised many of the mainstream Buddhist sects. When it was first introduced to Japan, from China, Buddhism was a very powerful force for stability and civilisation. The early Emperors in Kyoto engouraged the growth of the Buddhist faith because it brought with it a wealth of knowledge and it encouraged learning and good government in general.
However, over the centuries, the main Budhist sects became very powerful. They owned huge tracts of land, and commanded thousands of monks. Corrupt leaders were often tempted to use this power to extract concessions from the Emperor. Many of the largest temples even had their own armies of "soldier-monks", who would intimidate people who tried to interfere with their power.
Although Nichiren had a very positive influence on Buddhism, by condemning this sort of "unspiritual" behavior, his doctrine also had a rather dark side. His followers believed in an "apocalyptic" future, in which the Buddha would return to earth and destroy wickedness. There is reason to believe that the despair and harsh conditions that Nichiren experienced during his exile on Sado island may have had influenced him a great deal, and contributed to this "dark" side of his teachings.