The Han conquest of Gojoseon was a campaign launched by Emperor Wu of Han China against Wiman Joseon between 109 and 108 BC. It resulted in the fall of Gojoseon and the establishment of four Han commandaries in the Korean Peninsula.
King Ugeo of Gojoseon interrupted direct contact with envoys sent by chiefs of various tribes on the Korean Peninsula to the Han empire, thus Emperor Wu of Han dispatched the emissary She He (涉何) to Gojoseon. After an audience with the king, She He failed in securing the safe passage of the envoys. While returning to his nation, She He killed Wi Jang (長降), an assistant of the Gojoseon king. Due to this action, the king sent out troops to kill She He. The direct pretext for war thus came when King Ugeo had the Han envoy executed, which had angered Emperor Wu considerably.
However, the initiation of war may also have been brought by the desire to remove the possibility that Gojoseon would ally with the Xiongnu against the Han. Another reason may also have been the deteriorating relations between Han and Gojoseon, because Wiman Joseon prevented trade between Han and polities such as Jinbeon (진번, 眞番).
In 109 BC, Emperor Wu launched a Han military campaign into Gojoseon. Two forces—totaling about 50,000 troops led by Yang Fu (楊僕) and Xun Zhi (荀彘) respectively—set out from the Han empire to invade the kingdom. A navy sailed from Qi (present-day Shandong Province) across the Bohai Sea towards Gojoseon, while an army marched through Liaodong and headed towards Wanggeom, the capital of Gojoseon.
The initial stages of the Han military campaign into Gojoseon were unsuccessful, so Emperor Wu wished to reestablish peaceful relations between Han and Gojoseon. However, Gojoseon rejected the offer and strengthened their fortifications instead.  Eventually, the Gojoseon forces at Wanggeom surrendered to the Han. In 108 BC, all of Gojoseon had fallen and was conquered by Han.
After the conquest of Gojoseon by Han in the war, four Han commanderies were founded to administer the former Gojoseon territories. These were Lelang, Xuantu, Zhenfan, and Lintun. The most significant commandery was located in Lelang (near present-day Pyongyang), which controlled the region until 313 AD. The conquest of Gojoseon in 108 BC by Han, ultimately led to the Proto-Three Kingdoms period of Korea.