The Liaodong Peninsula is a peninsula in Liaoning Province of Northeast China, historically referred to in the West as Southeastern Manchuria. Liaodong once spelled Liaotung means "East of the Liao River"; alluding to the Liao River which separated the Yan commanderies of Liaoxi and Liaodong amid time of the Warring States time frame. The peninsula lies in the north of the Yellow Sea, between the Bohai Sea toward the west and Korea Bay toward the east.
It forms the southern piece of a mountain belt that continues northward in the Changbai Mountains. The piece of the mountain extend on the peninsula is known as the Qianshan Mountains, named after Qian Mountain in Anshan, which includes Dahei Mountain in Dalian. Liaodong went under the standard of the Gojoseon kingdom which developed in the locale. In the late 4th century BC, the Chinese State of Yan attacked and vanquished this district from Gojoseon.