The 1569 battle of Tatarahama was part of the struggles between the Ōtomo

Otomo clan

The Ōtomo clan was a Japanese clan whose power stretched from the Kamakura period through the Sengoku period, spanning over 400 years. The clan's hereditary lands lay in Kyūshū....

 and Mōri

Mori clan

The Mōri clan was a family of daimyō, descended from Ōe no Hiromoto and established themselves in Aki Province. Their name was derived from a shōen in Mōri, Aikō District, Sagami Province. The generation of Hiromoto began to name themselves Mōri.After the Jōkyū War, Mōri was appointed to the jitō...

 samurai clans during Japan's Sengoku period

Sengoku period

The or Warring States period in Japanese history was a time of social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The name "Sengoku" was adopted by Japanese historians in reference...

, for control of the island of Kyūshū

Kyushu

is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....

.

The battle took place in the aftermath of a successful siege by the Mōri of the Ōtomo's Tachibana castle

Tachibana castle

was a Japanese castle in Chikuzen Province, in the north of Kyūshū; it is located at the peak of Tachibana Mountain, extending in part into the Higashi-ku in Fukuoka...

, which sat just outside the boundaries of today's Fukuoka City

Fukuoka, Fukuoka

is the capital city of Fukuoka Prefecture and is situated on the northern shore of the island of Kyushu in Japan.Voted number 14 in a 2010 poll of the World's Most Livable Cities, Fukuoka is praised for its green spaces in a metropolitan setting. It is the most populous city in Kyushu, followed by...

. The two armies met on the shores of Hakata Bay

Hakata Bay

Hakata Bay is a bay in the northwestern part of Fukuoka city, on the Japanese island of Kyūshū. It faces the Tsushima Strait, and features beaches and a port, though parts of the bay have been reclaimed in the expansion of the city of Fukuoka...

, at Tatarahama, but were evenly matched, and both retreated.

In order to end the deadlock, the Ōtomo made an alliance with the Amago clan

Amago clan

The , descended from the Emperor Uda by the Sasaki clan .Sasaki Takahisa in the 14th century, having lost his parents at the age of three years, he was brought up by a nun...

. The Mōri clan's battles with this larger allied force occupied it to such an extent that Yamanaka Yukimori

Yamanaka Yukimori

, also known as Yamanaka Shikanosuke or Shikasuke , was a Japanese samurai of the Sengoku period, who served as a retainer to the Amako clan. Born under a crescent moon, he is known as the samurai of the crescent moon.-Further reading:...

 and Amago Katsuhisa

Amago Katsuhisa

was a remnant of the Amago clan, a powerful feudal clan in the Chūgoku region, Japan; backed-up by Yamanaka Yukimori, a vassal of the clan.He was born to Amago Masahisa in 1553. In the following year, Katsuhisa's father and grandfather were killed by Amago Haruhisa, leading Katsuhisa to become a...

, as part of their arrangement with the Ōtomo, were able to take Izumo province

Izumo Province

was an old province of Japan which today consists of the eastern part of Shimane Prefecture. It was sometimes called . The province is in the Chūgoku Region.- History :It was one of the regions of ancient Japan where major political powers arose...

, some distance away on Honshū

Honshu

is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...

, and that the Mōri became pressured into abandoning Tachibana.