According to Wikipedia:


Tokugawa Ieyasu January 31, 1543 – June 1, 1616) was the founder and first shogun of the Tokugawa shogunate of Japan which ruled from the Battle of Sekigahara in 1600 until the Meiji Restoration in 1868. Ieyasu seized power in 1600, received appointment as shogun in 1603, abdicated from office in 1605, but remained in power until his death in 1616. His given name is sometimes spelled Iyeyasu owing to the historical use of the we kana.

(Wikipedia contributors, "Tokugawa Ieyasu," accessed 2/16/08)

This reference first appears on page 191.
Ieyasu is another real historical refrence. Ieyasu is the general of Hideyoshi army. Robinson uses Ieyasu to keep the historical value of the people mention already.