Buddhism is well known as a peace loving religion. But in Japanese history, Buddhism was strongly linked to warfare in Japan. The battlefield was believed to be the realm where the gods and Buddhas mingled with men. Prayers were considered to be lethal weapons, and arms and armor were emblazoned with religious motifs. Some battles were fought in sacred places such as temple grounds and many of the largest and most powerful Buddhist temples had their own standing armies of warrior monks called sohei.
Victory revealed divine favor and the right to rule the realm. Because military prowess indicated otherworldly support, the powerful Ashikaga shoguns cast themselves as Buddhist kings.
Prayers were conceived as potent weapons. From the tenth century onward, the court monopolized prayers of destruction that were offered to five Buddhist deities (Fudo, Gozanze, Gundari, Dai-i-toku-ten, and Kongo), whose function was to protect the state. To pray to them was believed to magnify one's strength when fighting. "evil" and elaborate rituals were conducted to offer prayers.
These rituals were carefully monitored because they were believed to fatally undermine one's opponent. Therefore, it is no surprise that rebels also relied heavily on them. The first great shogun to confront the power of the court, Minamoto Yoritomo, initiated them during his 1180 uprising. Once the Minamoto bakufu was established, its officials attempted to monitor all spiritual activities of their potential enemies to prevent the maledictions that could foment disorder or threaten the rule of the Minamoto.
Buddhist symbols and imagery pervaded nearly every aspect of warfare. Banners of war were emblazoned with Hachiman daibosatsu, a god of war. Some warriors wrote the name of Jizo bosatsu on their armor, while others inserted Buddhist mandalas into their capes in order to provide for safety in this life and salvation in the afterlife.
The founder of the Ashikaga bakufu, Ashikaga Takauji, claimed to be particularly favored by Jizo bosatsu, a Buddhist avatar of compassion. Not only did he carry a small statue of the Jizo as a prized possession, but he communicated with Jizo through dreams which were well known to his enemies. The dreams of Jizo helped further Ashikaga Takauji's political image. He often drew pictures of Jizo and boasted of his ability to sense Jizo while dreaming. Takauji's religious aura was enhanced by his success on the battlefield.
For several hundred years through the middle ages and the warring states period, the warrior monks, called sohei, were a powerful force in Japan. They originally arose during political disputes between powerful temples. Later, they came to be involved in the major political disputes of the country. They would side with various powerful warlords in order to protect their interests. Vast armies of warrior monks played major roles in the rise and fall of shoguns and other warlords. However, it is not certain whether the sohei were actually Buddhist monks or were hired mercenaries. The sohei armies were finally crushed in the late 16th century by Oda Nobunaga.