The Alliance on the Sea was a political alliance in Chinese history between the Song

Song Dynasty

The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...

 and Jin (金) Dynasties in the early 12th century against the Liao Dynasty

Liao Dynasty

The Liao Dynasty , also known as the Khitan Empire was an empire in East Asia that ruled over the regions of Manchuria, Mongolia, and parts of northern China proper between 9071125...

. The alliance was negotiated from 1115 to 1123 by envoys who crossed the Bohai Sea

Bohai Sea

Bohai Sea , also known as Bohai Gulf, Bohai, or Bo Hai, is the innermost gulf of the Yellow Sea on the coast of Northeastern and North China. It is approximately 78,000 km2 Bohai Sea , also known as Bohai Gulf, Bohai, or Bo Hai, is the innermost gulf of the Yellow Sea on the coast of...

, and is also called the Alliance Conducted at Sea. Under the alliance, the two nations agreed to jointly-invade the Liao, split captured territories, cede the Sixteen Prefectures

Sixteen Prefectures

The Sixteen Prefectures are a region in northern China stretching from present-day Beijing westward to Datong. In most areas, it is approximately seventy to one hundred miles in width...

 to the Song, and forswore making unilateral peace with the Liao. In 1121-23, the Song faltered in their military campaigns but the Jurchen Jin succeeded in driving the Liao to Central Asia. The Jin handed over several of the Sixteen Prefectures to the Song including modern-day Beijing

Beijing

Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...

. In 1125, the alliance ended when the Jin, sensing weakness of the Song, invaded southward and eventually captured the Song capital of Kaifeng

Kaifeng

Kaifeng , known previously by several names , is a prefecture-level city in east-central Henan province, Central China. Nearly 5 million people live in the metropolitan area...

in 1127.