About The Unification Of Owari

In 1551, Oda Nobuhide (Nobunaga's Father) died unexpectedly and, during his funeral, Nobunaga was said to have acted outrageously, throwing the ceremonial incense at the altar. This act alienated many Oda retainers, convincing them of Nobunaga's mediocrity and lack of discipline and they began to side with his more soft-spoken and well-mannered brother, Nobuyuki. Hirate Masahide, who was a valuable mentor and retainer to Nobunaga, was ashamed by Nobunaga's behavior and performed seppuku. This had a huge effect on Nobunaga, who later built a temple to honor Masahide.

Though Nobunaga was Nobuhide's legitimate successor, the Oda clan was divided into many factions. Furthermore, the entire clan was technically under the control of Owari's shugo, Shiba Yoshimune. Thus Oda Nobutomo, as the brother to the deceased Nobuhide and deputy to the shugo, used the powerless Yoshimune as his puppet and challenged Nobunaga's place as Owari's new ruler. Nobutomo murdered Yoshimune when it was discovered that he supported and attempted to aid Nobunaga.

To increase his power, Nobunaga persuaded Oda Nobumitsu, a younger brother of Nobuhide, to join his side and, with Nobumitsu's help, slew Nobutomo in Kiyosu Castle, which later became Nobunaga's place of residence for over ten years. Taking advantage of the position of Shiba Yoshikane, Yoshimune's son, as the rightful shugo, Nobunaga forged an alliance with the Imagawa clan of Suruga Province and the Kira clan of Mikawa Province, as both clans had the same shugo and would have no excuse to decline. Additionally, this also ensured that the Imagawa clan would have to stop attacking Owari's borders.

Even though Nobuyuki and his supporters were still at large, Nobunaga decided to bring an army to Mino Province to aid Saitō Dōsan after Dōsan's son,Saitō Yoshitatsu, turned against him. The campaign failed, however, as Dōsan was killed and Yoshitatsu became the new master of Mino in 1556.

A few months later, Nobuyuki, with the support of Shibata Katsuie and Hayashi Hidesada, rebelled against Nobunaga. The three conspirators were defeated at the Battle of Inō, but they were pardoned after the intervention of Tsuchida Gozen, the birth mother of both Nobunaga and Nobuyuki. The next year, however, Nobuyuki again planned to rebel. When Nobunaga was informed of this by Shibata Katsuie, he faked illness to get close to Nobuyuki and assassinated him in Kiyosu Castle.

By 1559, Nobunaga had eliminated all opposition within the clan and throughout Owari Province. He continued to use Shiba Yoshikane as an excuse to make peace with other daimyo, although it was later discovered that Yoshikane had secretly corresponded with the Kira and Imagawa clans, trying to oust Nobunaga and restore the Shiba clan's place. Nobunaga eventually cast him out, making alliances created in the Shiba clan's name void.
Souce: Wikipedia