For most of the twentieth century, Nichiren Shoshu and the lay organization Soka Gakkai grew together so closely that a leading scholar of Japanese religion once compared them to Siamese twins, fused in a vital area, impossible to separate without real damage to both. Soka Gakkai supplied the overwhelming majority of the members, the money and the growth. Nichiren Shoshu supplied the priesthood, the head temple, and access to the Dai Gohonzon, the wooden mandala at the center of the tradition's most sacred doctrine.
The partnership ended in a specific month. Tension between Soka Gakkai's lay leadership and the Nichiren Shoshu priesthood had been building for over a year when, in November 1991, Taiseki-ji formally excommunicated Soka Gakkai and every one of its international chapters. Soka Gakkai rejected the order and denounced what it called the priesthood's appalling lack of respect for the faithful. The priesthood held its ground.
What the split actually divided, in the end, was custody. Taiseki-ji kept the temple, the priesthood, and the Dai Gohonzon itself, sole possession of the one object both sides had spent decades treating as central to their shared faith. Soka Gakkai kept millions of members worldwide and none of them access to it. A relationship built on sharing one object ended with one side holding it and the other side simply gone.