Editing Tokugawa Ieyasu (section)

=== Nobuyasu Incident ===
[[File:築山殿.jpg|thumb|Tsukiyama-Dono, wife of Ieyasu who was executed due to an accusation of treason]]
In 1579, [[Lady Tsukiyama]], Ieyasu's wife, and his heir Matsudaira Nobuyasu were accused by Nobunaga of conspiring with Takeda Katsuyori to assassinate Nobunaga, whose daughter Tokuhime was married to Nobuyasu. Ieyasu ordered his wife to be executed and forced his son to commit ''[[seppuku]]'' because of these accusations.<ref name="Ōoku The Secret World of the Shogun's Women; Tadatsugu Sakai">{{cite book |author1=Cecilia Segawa Seigle |author2=Linda H. Chance |title=Ōoku The Secret World of the Shogun's Women |date=2014 |publisher=Cambria Press |isbn=9781604978728 |url=https://books.google.com/books?id=nbF5CgAAQBAJ |access-date=6 May 2024 |language=En |quote=Notes 23= Tsukiyama-Dono pp. 85–86; Kinseishi p. 30}}</ref><ref name="Shogun The Life of Tokugawa Ieyasu; Lady Tsukiyama">{{cite book |author1=Arthur Lindsay Sadler |author1-link=Arthur Lindsay Sadler |title=Shogun The Life of Tokugawa Ieyasu |date=2004 |publisher=Tuttle Publishing |isbn=9781462916542 |page=53 |url=https://books.google.com/books?id=5HhzBgAAQBAJ |access-date=6 May 2024 |language=En}}</ref>

There are various theories regarding this incident. According to the "Mikawa Monogatari'", which was written by [[Ōkubo Tadachika]], Tokuhime, wife of Nobuyasu, who was not on good terms with her mother-in-law Tsukiyama-dono, wrote in a letter to her father, Nobunaga, that her mother-in-law and her husband were secretly conspiring with Takeda Katsuyori.<ref name="Tetsuo Owada 2002 24">{{harvtxt|Tetsuo Owada|2002|p=24}}</ref>

However, this hypothesis has been considered implausible by various historians in the modern era. According to Katsuhiro Taniguchi, the more plausible theory was that there was friction within the house of Tokugawa clan between two factions with conflicting ideals, as proposed by the writer Tenkyu Goro. One faction, dubbed the "Hamamatsu Castle Faction," was active on the front lines and had many opportunities to advance their careers. The other faction was the "Okazaki Castle Faction," which consisted of Tokugawa vassals responsible for logistical support due to past injuries and other factors that caused them to play a lesser role in the politics of Tokugawa clan. According to this theory, the conflict between these two factions eventually led to a conflict between Ieyasu, representing the Hamamatsu faction, and his son Nobuyasu, representing the Okazaki faction, finally ending with Nobuyasu's death in prison. Nobuyasu planned to exile Ieyasu with the help of the Okazaki Castle faction. Before and after his son's execution, Ieyasu punished or executed many of those who worked at Okazaki Castle, although some escaped. Taniguchi theorized that Tsukiyama also participated in the coup d'état that was going on in Okazaki Castle.{{sfn|Taniguchi|2007|pp=209–211}} Furthermore, Sakai Tadatsugu, the most prominent general of Ieyasu, also may have played a role in confirming Oda Nobunaga's suspicion of the alleged betrayal against the Oda clan being planned by Nobuyasu Tsukiyama. Ieyasu may have concluded that if a high-ranking [[fudai daimyō]] such as Tadatsugu had confirmed the accusations against Lady Tsukiyama, then they must be true.<ref name="Ōoku The Secret World of the Shogun's Women; Tadatsugu Sakai"/>

Another theory has said that Tadatsugu was actually conspiring with the Ieyasu's mother, [[Odai no Kata]], to get rid of Lady Tsukiyama.<ref name="Ōoku The Secret World of the Shogun's Women; Tadatsugu Sakai"/> [[Arthur Lindsay Sadler]] theorized this was a deliberate act of spite from Tadatsugu due to many senior Tokugawa clan generals' dislike of Nobuyasu.<ref name="Shogun The Life of Tokugawa Ieyasu; Lady Tsukiyama"/>

In the same year, Ieyasu named his third son, [[Tokugawa Hidetada]], as his heir, since his second son had been adopted by [[Toyotomi Hideyoshi]], who would later become a powerful daimyo.{{Citation needed|date=March 2020}}