The structure of the Shin Buddhist sect in Japan that we see today are a direct result of the actions of Oda Nobunaga 430 years ago.
Shin Buddhism is the dominate form of Buddhism in Japan today. Did you know that Shin Buddhism in Japan is split into an East or Higashi Honganji branch and a West or Nishi Hongwanji branch? Up until the late 16th century, the Shin sect was unified into one powerful sect of Buddhism. The Shin sect was one of the major power players in Japan at that time along with the powerful warlords. After Tokugawa Ieyasu's victory at the Battle of Segigahara, Ieyasu split the Shin sect in two in order to restrict their power.
What I did not know was that the East and West split actually began to happen in 1580 after Oda Nobunaga finally defeated the Shin Buddhist armies of the Ikko Ikki. Nobunaga's battles with the Ikko Ikki lasted for ten long years. The Ikko Ikki were led by their leader Kennyo who resided in the temple fortress Honganji near present day Osaka.
In 1580, after several years of resisting from their citadel stronghold Honganji, Kennyo finally realized that peace was the only way for their survival. Kennyo agreed to surrender the citadel to Nobunaga's forces. In May of 1580, Kennyo retreated from Honganji with a small party of followers a full three months before Nobunaga's deadline for surrender. During that time, Kennyo entrusted the Honganji to his son Kyonyo.
Kennyo was convinced that his Shin sect would be completely destroyed by Nobunaga if they continued to resist, but a rival group centered around Kyonyo were strongly opposed to vacating the Honganji temple fortress and were determined to make one final stand. Kyonyo and his followers were reluctant to hand over what had been hallowed ground and they distrusted Nobunaga. However, Nobunaga's army slowly squeezed Honganji, isolating it from the outside world, and gradually increased the military pressure on Kyonyo.
Finally, Kyonyo also realized the futility in resisting and surrendered in September of 1580. According to the book, Japonius Tyrannus, Kyonyo was heavily at odds with his father after these events. Kennyo disowned his son Kyonyo and appointed a younger son as his successor instead, causing a family rift that would ultimately lead to the division of the Honganji into a western and an eastern branch under Ieyasu. The eastern branch was led by Kyonyo while the western branch was led by Kennyo's third son Junnyo.