Sulfur

• Other Names: sulphur
• Japanese: 硫黄 (iou)

Sulfur is a yellow mineral essential to the production of gunpowder.

One of the chief sources of sulfur historically in the region around Japan was the island of Iô Torishima, located in the Amami Islands to the south of Kyushu and controlled by the Ryûkyû Kingdom throughout the Edo period. China imported sulfur from the kingdom as well as from other sources, but forbade the export of the material. This made trade relations with (or control of) Ryûkyû vital for military preparedness, and powers throughout the region regularly worked to secure or maintain sources of Ryûkyûan sulfur. Ryûkyû often traded sulfur to entities in Japan, Korea, and China, or presented it as tax or tribute; in trade with Southeast Asia, however, Ryûkyû only ever shipped sulfur to Siam, and not to other polities. Japanese entities such as the Heian court and Muromachi shogunate exported a portion of the Ryûkyûan sulfur they obtained, in sizable enough amounts that sulfur is noted as one of the chief exports of premodern Japan.

In the 1420s to 1510s, Ryûkyû shipped on average 27-37,000 jin (J: kin) of sulfur to China each year. For various reasons, this amount declined from roughly 35-38,000 jin in the 1420s-1470s to 27-28,000 jin in the 1470s to 1510s, and then to only 6-8,000 jin in the 1510s-1600s.

Following the Shimazu invasion of Ryukyu in 1609, despite the great importance of sulfur for the Shimazu armies, the Shimazu allowed Ryûkyû to maintain control of Iô Torishima, even as they extended their own administration over the remainder of the surrounding (Amami and Tokara) islands. This was likely done in large part in order to allow Ryûkyû to continue to send sulfur as a tribute good to China, thus allowing for the maintenance of the tributary relationship which was the essential core of Ryûkyû's value to the Shimazu to begin with.