Yoritomo grows increasingly suspicious of his half-brother, the brilliant military strategist Yoshitsune, who had finally fled to the north and, in 1189, committed hara-kiri at the age of thirty.

In 1191, Yoritomo goes to Kyoto to visit the Japanese emperor, who, threatened by the emergent samurai class represented by the Minamotos and others, appoints him Sei-i-tai-Shogun (generalissimo) for life.

Yoritomo is the first to receive this title, an emergency post granting military command powers for the purpose of conquering barbarians.

Although the shogun is nominally under imperial command, the fact that he can make the unilateral decision to move armies renders the shogun the supreme entity.