Mori Motonari was born on 14 March 1497, the son of Mori Hiromoto, the lord of Yoshida Manor in Aki province. His mother, Sachi, named him Shojumaru. As a child young Shojumaru watched his father struggle against the rival warlords. The Chogoku district at that time was dominated by two major clans: the Ouchi and the Amako, who contested the area. Because of the power of these two clans the other daimyos were forced to submit to one or the other for protection.

The Mori domains were small, producing less than 1,100 kilograms of rice, and incapable of producing a big army. In desperation Hiromoto became Ouchi Yoshioki's vassal. After numerous battles, Hiromoto became tired of fulfilling his duties as vassal.

Meanwhile, the Shogun, Ashikaga Yoshitane, was expelled from Kyoto following the Battle of Shogakuji in 1491 and fled to Ouchi for protection. In 1499 Yoshioki decided to restore the shogun to power and the Moris were asked to accompany them to the capital. The Shogunate under the usurper Yoshizumi, however, ordered the Moris to attack the Ouchi. Hiromoto was unable to defy such an order and contemplated resigning his position in favor of his first son, Kochiyomaru (soon to be Okimoto). Shojumaru grew increasingly antagonistic towards his father, who meanwhile was fighting a losing war against the Amako, and had let himself become addicted to sake.

In 1500 the rulership of the clan was passed over to Kochiyomaru and Hiromoto retired with his wife and Shojumaru to Sarukake. The next year Sachi died. Shojumaru was crushed by the loss of his mother. His father remarried Sugi and increased his drinking, and for the most part, ignored his son.

At the age of ten Shojumaru's father died from complications due to excessive drinking. The young lord now became master of his father's castle. Over the next years he grew closer to his new mother, while learning the ropes of leadership. His older brother, Okimoto, whom he had respected since childhood, soon returned to his side. In 1511, at age fifteen Shojumaru received a new name, Motonari.

Ouchi again pressed the Mori for aid in his march on Kyoto. Previously Hiromoto had asked Ouchi Yoshioki to be the godfather of Kochiyomaru; now the Moris were obligated to comply. However, Okimoto soon left Ouchi's service. Betrayed, the Ouchi nevertheless won a smashing victory outside Kyoto and restored Yoshitane to power.

The Mori's were now in fear of Ouchi's wrath and therefore reinforced their position by marriage. Okimoto took the daughter of Takahashi Motoshige as his wife and this strengthened bond between the Mori, Amano, Kikkawa, and Takahashi families. The tactic worked and the Moris enjoyed years of relative peace. Okimoto gave birth to a son, whom he named Komatsumaru.

However, the peace did not last long. A rival warlord named Takeda Motoshige, who had made secret negotiations with the Amako, suddenly attacked Ouchi and captured his capital at Koi. Soon Motoshige was marching into the Mori domains. Okimoto gathered his allies and fought the enemy. It was Motonari's first battle. The Mori won, but in the process Okimoto was killed, leaving behind his two-year-old son a successor. In 1517 Takeda returned again and Motonari for the first time took command the army. At Arita on October 22, 1517 the Takedas were decisively defeated. The victory sped in motion the Mori's rise to power. Motonari eventually took over control of the clan. Over time Motonari had three sons: Takamomo, Motoharu, and Takakage. There is a famous parable that Mori invited his sons to each break an arrow and then demonstrated the difficulty of breaking them all at once. "So it must be with you," he stated. An example of this is shown in the movie Ran.

New Overlord

From 1539-1541 Mori fought alongside the Sue against the Amako on behalf of the new overlord, Ouchi Yoshitaka, whose father, Yoshioki, had passed away in 1524. At Aki-Koriyama Mori beat off an attack by the Amako. Afterwards the conflict died down in 1543 Ouchi attacked the Amako at Toda and was bitterly defeated. Afterwards, Yoshitaka grew careless and devoted his time to pleasure rather than defense. Both Mori and Sue urged their lord to strengthen his position for fear of a coup. Ironically it was Sue who staged that coup.

Mori plotted revenge on the Sue, but waited for an opportunity. In 1554 that opportunity came and Mori went to war against the Sue. Mori's generals encouraged him to fortify the holy island of Itsukushima and he agreed. A castle was soon built called Miyajima and Motonari began spreading rumors about its lack of defense—enticing the sue to capture it. Sue fell for the bait and took the castle in 1555. Meanwhile, Motonari captured Kusatsu and cut off Sue's retreat. The Sue were now trapped, but with odds stacked against the Mori, Motonari decided to launch a surprise attack on the island.

At night during a rainstorm Motonari and two of his sons landed on the island, while his other son landed behind the island. At dawn they attacked from front and rear, destroying the Sue, who were caught offguard. The victory had displaced the Sue and left the Mori in complete control of the Chogoku area. Eventually in 1557 the last of the Ouchi's, Yoshinaga, was forced to commit seppuku as the Mori's advanced on him.

In 1558 Motonari took Moji castle, thus gaining a foothold in northern Kyushu. Otomo Yoshishige (Sorin) could not allow this and he took an army to retake the castle the next year—war thus began between the two clans. In 1560 the Mori again took the castle. Otomo attempted to retake the castle again that year, but was defeated by the Mori navy.

In 1561 Otomo gathered a massive force to storm Moji. He realized that the castle would be difficult to take by land because its defenses had been bolstered by the presence of the Mori fleet. Otomo, however, convinced the Portuguese to aid him. Three Man of War bombarded the castle. The castle would have fallen, but the cannons soon ran out of ammo. The bombardment of the garrison was watched by Takakage and Takamoto, but they could not act because of the firepower of the European ships. When the ships did retire, the two Mori sons sent relieving forces across the straight and fought their way into the castle. Otomo then ordered an all-out attack on the castle, but the Mori repulsed them at all points. Otomo was forced to withdraw.

In 1562 Mori and the Amako went to war. The campaign primarily focused on the Amako capital at Toda. Several attempts to take the castle were met with defeat, but finally in 1565 the outer defenses fell. In November 1566 the Amako surrendered. In 1570 a decisive battle over the Amako was won at Nunobeyama, but, the war would continue for many years to follow.

In 1568 Motonari came to the aid of Kono Michinao in his fight against Utsunomiya Toyotsuna. A great victory was won at Torisaka and Kono was reinstated in his domains. Meanwhile the war continued with the Otomo. That same year at Tatarahama, Otomo's vassal, Hetsugi Akisura, was defeated by Takakage, and later the castle of Takibana fell.

The old warrior finally crossed the jaded pavilion in 1571. From a humble origin he had extended the Mori name over ten provinces in Chogoku, and parts of Buzen and Iyo. He had fought in over 200 battles and made the Mori the leading warlord in Japan's warring states period. The katana was passed to grandson, Terumoto, who continued to expand the Mori name. He would bear the brunt of Nobunaga's advances and clash with him several times. Following Nobunaga's death he made peace with Hideyoshi, aided him in unifying the country, subduing Korea, and fighting for the Toyotomi at Sekigahara.