The daimyo
Regional warlords, the daimyo, fought each other for land, built castles and made their own laws. The period takes its name, Sengoku, from China’s own era of Warring States.
In 1543 Portuguese traders reached Japan, and with them came firearms, which Japanese smiths were soon making for themselves. In 1549 the Jesuit Francis Xavier arrived, and Christianity began to spread, especially in the southwest.
Oda Nobunaga
Nobunaga seized Kyoto in 1568 and installed Ashikaga Yoshiaki as shogun. In 1573 he drove Yoshiaki out, which ended the Ashikaga shogunate. Nobunaga was killed in 1582 at the temple of Honnō-ji in Kyoto, betrayed by one of his own generals, before the work was done.
Toyotomi Hideyoshi
His successor Hideyoshi, who had risen from humble origins, completed the unification by 1590. He never became shogun. He ruled instead as kampaku, the imperial regent, a title from the old court, and later as taikō, retired regent. His lack of noble descent is the usual explanation, though historians still debate it.
Hideyoshi invaded Korea in 1592 and again in 1597. He died in 1598, leaving a five year old son, Hideyori, and a council of regents to govern for him. That council is where Clavell’s novel begins.
Tokugawa Ieyasu
The most powerful of the regents was Tokugawa Ieyasu, lord of the Kanto plain. In 1600 he defeated the coalition led by Ishida Mitsunari at the battle of Sekigahara, and in 1603 the emperor made him shogun. A saying has it that Nobunaga mixed the rice cake, Hideyoshi kneaded it, and Ieyasu ate it.