The "Age of Warring States" of feudal Japan.
The Onin War tore Japan apart, but also kicked off the Sengoku Jidai or Warring States Period that's a seminal part of Japanese history. The power of the shogun dissolved and regional clan leaders or daimyo fought for control of the country. In the mid 16th century, near Kyoto, a clan called the Matsudaira found itself pinched between two great rivals: the Oda and the Imagawa. Abducted as a hostage by the Oda, the scion of the Matsudaira clan (the young Tokugawa Ieyasu) grew up to fight alongside of the Imagawa when he was released. Their combined forces threatened to destroy the entire Oda clan, but Oda Nobunaga had a different idea. They clashed at the Battle of Okehazama.
With his western borders secure, Oda Nobunaga turns his attention east in the direction of the Shogun. When diplomacy fails to subdue the Saito clan that stands between him and Kyoto, Nobunaga enlists the aid of his brilliant diplomat and engineer, Toyotomi Hideyoshi. Toyotomi turns the Saito's vassals against them and constructs a fort for Nobunaga's samurai to siege Inabayama Castle. After his crushing victory, Nobunaga allies with the former Shogun's brother and uses him as a political shield to take Kyoto.
Now that he holds Kyoto, Oda Nobunaga finds himself the focus of enemies on all sides. Even the Shogun, who no longer needs his military assistance, turns against him. Oda marches north to quell the Asakura clan, only to be betrayed by the Azai clan leader, his own brother-in-law, who allies with his enemy and embroils Oda and his remaining true ally, Tokugawa Ieyasu, in the Battle of Anegawa. No sooner has he won a narrow victory than Oda launches into in an eleven year siege with the Ikko-ikki warrior monks at their mountain temple of Hongan-ji. Unable at first to turn that siege in his favor, he learns from it when facing a second group of Enryaku-ji warrior monks at Mount Hiei. Oda shows his true brutality by setting fire to the temple and ordering his troops to massacre all 20,000 inhabitants - men, women, and children.
Oda Nobunaga's control of Japan grows shakier by the day as more rivals emerge to challenge his hold on Kyoto. Egged on by the puppet shogun, Ashikaga Yoshiaki, the powerful daimyo Takeda Shingen brings his army down upon Oda's closest ally, Tokugawa Ieyasu, and destroys them, Tokugawa escapes with his life and the aid of a ninja, Hattori Hanzo, whose subterfuge succeeds in turning back the Takeda forces. They return under Takeda's heir, however, to besiege Nagashino Castle. Tokugawa's forces hold out until a lowly footman named Torii Suneemon gives his life to bring Oda and Tokugawa reinforcements back to the troops at Nagashino. Oda's innovative strategy with his arquebusiers defeats the famous Takeda cavalry charge and wins the day, but his military victories do nothing for him in the end. His own general, Akechi Mitsuhide, leads his army against him in a surprise attack at the temple of Honno-ji. Rather than be captured, Oda Nobunaga commits seppuku.
With Oda Nobunaga dead, Japan hangs in the balance. His old retainer, Tokugawa Ieyasu, must flee for his life from the usurper Akechi Mitsuhide. He narrowly escapes with the help of his ninja ally Hattori Hanzo, but Oda's heir is not so lucky: Akechi assassinates him. With power up for grabs, Toyotomi Hideyoshi sweeps into Kyoto and destroys the usurper, then appoints a puppet heir to replace Oda Nobunaga while he truly rules Japan. Toyotomi, today known as a great unifier whose reign is called the Momoyama Period, enacts three policies to reinstate taxes, eliminate banditry, and instill a rigid social caste system. He succeeds in restoring national civil government to Japan, signalling the beginning of the end for the Sengoku Jidai. But Tokugawa Ieyasu waits in the wings...
After Toyotomi Hideyoshi passes from old age, control of Japan passes to his young son - or more accurately, to his council of advisors. Tokugawa Ieyasu, the most powerful among them, looks poised to seize power for himself, but a rival named Ishida Mitsunari plots against him. After his first treacherous plot is discovered and foiled, Ishida joins with Uesugi Kagekatsu to mount a campaign against Tokugawa. An old friend, Torii Mototada, gives his life to counter the campaign and buys Tokugawa enough time to defend himself. The defection of the Kobayakawa clan from Ishida broke this opposition once and for all, leaving Tokugawa in uncontested control of Japan. Though he became shogun, Tokugawa ruled for only two years before passing succession to his son, establishing for the first time not only a stable shogun but a stable chain of succession, and bringing Sengoku Jidai period to an end in Japan.