Emperor Wu, having secured his northern and western frontiers, sent an army and fleet against Wiman Joseon in 109 BCE; after a siege the capital Wanggeom fell in 108 BCE and the kingdom was abolished. Four commanderies were established in its place, the most durable being Lelang near modern Pyongyang, which functioned as a Chinese administrative and commercial enclave on the peninsula for four centuries and left a rich archaeological record of Han-style tombs and artefacts. The Han motive recorded in the sources was strategic and economic — removing a state that obstructed contact with the peoples further south, and gaining access to iron and salt. Displaced elites and commoners from the destroyed kingdom moved south, contributing to the formation of the later Korean polities. The extent of Chinese settlement, and how far Lelang was a colony of immigrants rather than an administration imposed on a local population, remain matters of scholarly and nationalist dispute.
Emperor Wu of Han destroyed Wiman Joseon in northern Korea and replaced it with four directly administered Chinese commanderies
The Book of Han's census of 2 CE records 406,748 people in 62,812 households in Lelang commandery and about 221,845 in Xuantu, the two surviving commanderies of the four founded in 108 BCE. The count is a tax register taken a century after the conquest and covers registered households only, so it is a floor rather than a full population.
No usable figures. The sources describe a year-long campaign with a siege and internal assassination of the Joseon king rather than mass killing of the population, and give no casualty totals.
North Korea, South Korea