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Invaded Japan to cut sulfur
The Sulfur Supply
The Song had lost their sources in northern China and got their sulfur from Japan. Cutting that trade had other benefits. A Song court that could trade with Japan could also flee there, and a conquered Japan might scare the south into surrender.
A Failed Landing
The invasion itself went badly. His ships were good on rivers and along the coast, and they struggled across treacherous water. Trebuchets and grenades on a beach did little damage, since Japanese cities were not sitting on the shore, and the Mongols did not have enough horses. The samurai rode out and recited their genealogies, a ritual the Mongols had no use for, and the Japanese defeated them.
The Objective Achieved
Kublai Khan failed to conquer Japan and still got what he was after. His navy ruled the water, trade stopped, supplies stopped, and the Song court could no longer flee to Japan. The fleet also gained experience with the ocean, and it moved on toward the coast of southern China.
Why does gunpowder need sulfur?
Black powder is a mix of saltpeter, charcoal, and sulfur, typically in proportions of about 75, 15, and 10 percent. Sulfur lowers the temperature at which the mixture ignites and helps it burn fast. Without it, the powder burns weakly. Sulfur came from volcanic regions, and Japan has many volcanoes.
Why did Japan export sulfur to China?
Japan sits on volcanic islands, and sulfur deposits were common there. Sulfur was one of the goods Japan shipped to China from at least the Song period. Chinese court records list it among the products Japanese traders brought. The Song state, which used gunpowder weapons heavily, depended on the trade.
What ended the first Mongol invasion of Japan?
The first invasion came in November 1274, when a fleet carrying Mongol and Korean troops landed near Hakata Bay. The Japanese defenders fought mostly in single combat, while the Mongols fought in formation and used grenades. After a day of fighting the invaders withdrew to their ships. A storm that night wrecked many of them.
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