Byeonhan, also known as Byeonjin, was a loose confederacy of chiefdoms that existed from around the beginning of the Common Era to the 4th century in the southern Korean peninsula. Byeonhan was one of the Samhan (or "Three Hans"), along with Mahan and Jinhan. 
Archaeological evidence indicates an increase in military activity and weapons production among the Byeonhan in the 3rd century, especially an increase in iron arrowheads and cuirasses (Barnes 2000). This may be associated with the decline of Byeonhan and the rise of the more centralized Gaya Confederacy, which most Byeonhan states joined. Gaya was subsequently annexed by Silla, one of the Three Kingdoms of Korea.
The Chinese Records of Three Kingdoms state that the language and culture of Byeonhan was essentially the same as Jinhan, and archaeological artifacts show little difference. Byeonhan may have simply referred to the chiefdoms in the south and west of the Nakdong River valley which were not formal members of the Jinhan confederacy.