The real book is set by the following problem: what significance did Zen Buddhism have for Japanese warriors of the Middle Ages and our time? How did he change them? Why did warriors striving for perfection profess this particular form of Buddhism? After all, Buddhism, no matter what forms it takes in a particular country, remains primarily a religion of compassion. Never in its long history has Buddhism been associated with war. How then could it happen that Zen strengthened the morale of a Japanese warrior? How could it happen that Zen entered the blood and flesh of the Japanese military class and became inseparable from the samurai spirit?