What is happening in Korea in 200BCE
Iron working was introduced into the Korean peninsula in the 4th century BCE. At around the same time, the first historically-known kingdom arose in the region, in the north. This was Gojoseon, and it appears in contemporary Chinese records as a trading partner and military opponent of states in northern China.
In fact, Gojoseon was probably only one of a number of tribal kingdoms that arose in the peninsula at this time. These states were centred on small walled towns, and were probably confederacies of smaller chiefdoms under the leadership of a powerful leader, or king. Gojoseon expanded into a league of such kingdoms (it is referred to as a “confederated state” by the Chinese) covering a large area of northern Korea.
All this was linked to the coming of horses and chariots to Korea, and the more organized warfare that this necessitated. Iron weapons also made their appearance.