The Mikuni Pass [ja] separated the Kantō region from Echigo Province in ancient Japan. As such, it has long been used as a major transportation hub for travelers going between those two areas. During the Edo period, the Mikuni Kaidō was established with the purpose of helping daimyō who were participating in sankin kōtai, which required daimyō to spend a portion of their time in Edo.
In 1902, the Shin'etsu Main Line was built, the first train line through the area. As a result, the economies of many of the post towns began to falter. However, the area between Nagaoka and Yuzawa was able to continue to flourish because the flat land allowed them to pursue agriculture. The area across the Mikuni Pass, however, received very little traffic.
In 1953, as cars became more common, so did long-distance transport, which led to a great rise in traffic in the area. However, for cars traveling between the Kantō and Echigo regions, it was very inconvenient to take the same detour as the train line, so the prefecture began major repair and construction work along the Mikuni Kaidō.
