The northern region of the Korean peninsula…

The northern region of the Korean peninsula and Manchuria had been occupied by the nascent states of Buyeo, Goguryeo, Okjeo, Dongye, and other minor statelets after the defeat of Gojoseon by China's Han dynasty of China in 108 BCE.

Goguryeo's traditional founding date is 37 BCE, but it is mentioned in Chinese records as early as 75 BCE, or possibly even the second century BCE.