Otomo Yoshishige, who adopts the name of "Sambisai Sorin” in 1562, is best known as "Otomo Sorin".

The Otomo clan during this same year accepts an alliance with the Amako (who are the enemies of the Mori), against the Mori.

Môri Takamoto, the current head of the Mori, is assisted by the Shôgun Ashikaga Yoshiteru, which leads to a peace treaty between the clans.

Sorin, to prove that there will be peace, proposes that his daughter be married toTakamoto's son Mori Terumoto, though it is unclear whether this union actually occurs.

Otomo Sorin suppresses a rebellion by the Akizuki of Chikuzen in 1564, then moves against the Ryuzoji of Hizen, which prompts the interference of the Mori.

Otomo Sorin has meanwhile received the news that Hetsugi Akitsura, a notable vassal of the Otomo, had been defeated at the Battle of Tatarahama and has lost the Tachibana Castle.

Sorin now threatens the Mori‘s Buzen foothold, forcing the clan’s retreat.

He is by this time is in control of Bungo, most of Buzen, Chikuzen, Chikugo, and wields influence over Higo and Hizen.

The Mori family had first achieved prominence in the early sixteenth century when some vassals of the Ouchi family, then the dominant power in west Honshu and probably the most powerful warriors in all Japan, had revolted against the Ouchi's autocratic rule.

Under the leadership of Mori Motonari (1497–1571), his family, though not directly involved in the uprising, had been able to profit by the revolt, and in 1557 he had become the new overlord of west Honshu.

Motonari's grandson, Mori Terumoto, had become the major opponent of Nobunaga when the great warrior made his bid to reunify Japan.

After a two-year siege against Bessho Nagaharu, a retainer of the Mori clan, the Hideyoshi clan in 1580 captures Miki, a city in western Honshu, Japan, that had developed around a castle built by Bessho Naganori in 1468.

Nobunaga, having conquered central Japan by the spring of 1582, is attempting to extend his hegemony over western Japan.

He has overthrown the old order of fractionized power held by the daimyo and has paved the way for the political and economic unification of a country rent for over a century by incessant civil warfare.

Having brought nearly half of the provinces of Japan under his control, he has nearly succeeded in unifying Japan when he is wounded in June 1582 at Honnoji Temple during the rebellion of discontented vassal Akechi Mitsuhide and commits suicide.

Hideyoshi, his most brilliant general, quickly avenges the death by defeating Mitsuhide at the Battle of Yamazaki and moves to assume Nobunaga's preeminent political position.

Mori Terumoto makes peace with Hideyoshi, whose trusted general he becomes.

Hideyoshi is appointed kampaku (chancellor to the emperor) in 1585 and soon becomes dajo-daijin (chief minister).

Awarded the family name of Toyotomi by the emperor, he thus comes to bear the name Toyotomi Hideyoshi.

He soon makes peace with Mori Terumoto, who had again become his antagonist.

The powerful warlord Mōri Terumoto establishes Hiroshima on the river delta coastline of the Seto Inland Sea in 1589, making it his capital after leaving Koriyama Castle in Aki Province and quickly building Hiroshima Castle, thus essentially founding Hiroshima.

Today the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshū, the largest island of Japan, Hiroshima is also to become the first city in history destroyed by a nuclear weapon when the United States of America drops an atomic bomb on it at 8:15 AM on August 6, 1945, near the end of the Second World War.

Mitsunari meets in his home Sawayama Castle with Ōtani Yoshitsugu, Mashita Nagamori, and Ankokuji Ekei.

Here they forge the alliance and invite Mōri Terumoto, who actually does not take part in the coming great battle, to be its head.

Most clans are content with their new status, but there are many clans, especially those on the western side, who become bitter about their displacement or what they see as a dishonorable defeat or punishment.

Three clans in particular do not take lightly the aftermath of Sekigahara:

• The Mōri clan, headed by Mōri Terumoto, are to remain angry toward the Tokugawa shogunate for being displaced from their fief, Aki, and being relocated to the Chōshū Domain, even though the clan had not taken part in the battle at all.

• The Shimazu clan, headed by Shimazu Yoshihiro, blames the defeat on its poor intelligence-gathering, and while they are not displaced from their home province of Satsuma, neither do they they become completely loyal to the Tokugawa shogunate.

Taking advantage of its large distance between Edo and the island of Kyūshū as well as its improved espionage, the Shimazu clan is to demonstrate that it is virtually an autonomous kingdom independent from the Tokugawa shogunate during its last days.

• The Chōsokabe clan, headed by Chōsokabe Morichika, is stripped of its title and domain of Tosa and sent into exile.

Former Chōsokabe retainers will never quite came to terms with the new ruling family, the Yamauchi clan, which will make a distinction between its own retainers and former Chōsokabe retainers, giving them lesser status as well as discriminating treatment.

This class distinction is to continue even generations after the fall of the Chōsokabe clan.

The descendants of these three clans will in two centuries collaborate to bring down the Tokugawa shogunate, leading to the Meiji Restoration.