The Liáodōng Peninsula (simplified Chinese: 辽东半岛; traditional Chinese: 遼東半島; pinyin: Liáodōng bàndǎo) is a peninsula in the Liaoning province of northeastern China, historically known in the west as southern east-Manchuria. Liaodong (formerly spelled Liaotung) means "East of the Liao". The Liao River was a river during the Warring States that divided the Yan commandries of Liaoxi (simplified Chinese: 辽西; traditional Chinese: 遼西) (west of the Liao) and Liaodong.

The peninsula is situated at the north of the Yellow Sea, between the Bohai Sea to the west and the Korea Bay to the east.

It forms the southern part of a mountain belt that continues northward in the Changbai Mountains. The part of the mountain range on the peninsula is known as the Qianshan Mountains, named after Qian Mountain in Anshan, which includes Dahei Mountain in Dalian.

There are two seaports: Dalian, which lies midway along the peninsula at its narrowest point, and Port Arthur/Lushun (now part of Dalian City), which is located at its southernmost point. Lüshun/Port Arthur has a large lake-like naturally-protected harbor and semi-sheltered outer roadstead making it very attractive to imperialist powers at the end of the nineteenth century. Dalny/Dairen/Dalian's harbor required greater investment, initially supplied by the Russians, but turned into a first class city under the Japanese period of administration (1905–1945). The two ports are about 25 miles (40 km) apart by rail, but about 40 nautical miles (70 km) apart by sea. Lüshun is 550 rail miles south of the Manchurian railroad hub city of Harbin on the historic Southern Manchurian Railway (today's China Far East Railway (CER), which construction was one of the underlying causes of the Russo-Japanese War).

Yeon Gaesomun (Hangeul:연개소문 Hanja:淵 蓋蘇文 or 伊梨 柯須弥)(603–666) was a powerful and controversial military dictator and Generalissimo^{[citation needed]} in the waning days of Goguryeo, which was one of the Three Kingdoms of ancient Korea. Yeon is also remembered for a number of successful resistance in military conflicts with Tang Dynasty under Emperor Li Shimin and his son Emperor Gaozong. Their failure to Yeon was the only defeat that Emperor Li Shimin ever suffered on the battlefield.

Traditional Korean histories paint Yeon as a despotic leader, whose cruel policies and disobedience to his monarch led to the fall of Goguryeo. However, his achievements in defending Goguryeo against Chinese onslaughts have inspired Korean nationalist historians, most notably the 19th century Korean historian and intellectual Shin Chaeho, to term Yeon the greatest hero in Korean history. Many Korean scholars today echo Shin and praise Yeon as a soldier-statesman without equal in Korean history, though other scholars strongly disagree. Chinese and Japanese scholars continue to hold an unfavorable view of Yeon^{[citation needed]}.

Buyeo or Puyŏ (Korean pronunciation: [pujʌ]), Fuyu in Chinese, was an ancient Korean kingdom located from today's Manchuria to northern North Korea, from around the 2nd century BC to 494. Its remnants were absorbed by the neighboring and brotherhood kingdom of Goguryeo in 494. Both Goguryeo and Baekje, two of the Three Kingdoms of Korea, considered themselves its successor nation.

Although records are sparse and contradictory, it is speculated that in 86 BCE, Dongbuyeo (Eastern Buyeo) branched out, after which the original Buyeo is sometimes referred to as Bukbuyeo (Northern Buyeo). Jolbon Buyeo was a small tribal state situated in north of the Korean peninsula and Manchuria. According to Samguk Sagi, in 504, the tribute emissary Yesilbu mentions that the gold of Buyeo can no longer be obtainable for tribute as Buyeo has been driven out by the Malgal and the Somna and absorbed into Baekje. It is also shown that the Emperor Shizong wished that Buyeo would regain its former glory. In 538, long after the fall of Buyeo, Baekje renamed itself Nambuyeo (Southern Buyeo).