The Battle of Sekigahara (1600) was one of the largest samurai battles. It was fought over Hideyoshi's successor.
Hideyoshi had an heir in 1593, only a few years before he would die, and he left five trusted men in charge until his son, Hideyori, was able to take over. Among the five men was Tokugawa Ieyasu, who was not loyal to Hideyori.
All of the major samurai clans took sides, some remaining loyal to Hideyori, while some chose to rebel against him.
This battle would allow Ieyasu to gain power and take over Japan, and became the shogun in 1603 (Gates, "Samurai").
