Why did Japan's emperors end up ruled by generals?

Japan's emperors ended up ruled by generals because, in the late 12th century, one warrior won a civil war and made himself the real government. Before that, civilian power belonged to the emperor and his regents, drawn from the court and the aristocratic clans around it. Then Minamoto no Yoritomo defeated the rival Taira clan in the Genpei War. He had promised lands and administrative rights to warriors who swore allegiance to him.

Yoritomo did not seize the throne. He built a separate military government at Kamakura and took the title of shogun, which began as the name of a general sent to fight the tribes of northern Japan, and after the twelfth century came to mean the leader of the samurai. The emperor and his court in Kyoto stayed in place, but as figureheads. Historians even disagree on the exact start date: some give 1192, when Yoritomo was named shogun, and others 1185, when he set up military governors and stewards.

The system had a clever disguise. The government was called the bakufu, the "tent government", because a tent was the headquarters of a field commander and was meant to be temporary. Yet after Yoritomo died, even the shoguns lost control. The Hōjō family, his wife's relatives, became regents who ran everything. His widow, Hōjō Masako, was so powerful that people called her the "nun shogun". The result was a pyramid of usurpation: the Hōjō had taken power from the Minamoto, who had taken it from the emperor, and everyone kept their titles.

That pyramid lasted 135 years, and the idea of a shogun beside the emperor survived for nearly 700.