Excerpts from Books and Wikipedia
"The Genpei War (...) was a national civil war between the Taira and Minamoto clans during the late-Heian period of Japan. It resulted in the downfall of the Taira and the establishment of the Kamakura shogunate under Minamoto no Yoritomo in 1192. . . . It followed a coup d'état by the Taira in 1179 with the removal of rivals from all government posts, and subsequently banishing them, and a call to arms against them, led by the Minamoto in 1180. The ensuing battle of Uji took place just outside Kyoto, starting a five-year-long war, concluding with a decisive Minamoto victory in the naval battle of Dan-no-ura. . . . . The end of the Genpei War and beginning of the Kamakura shogunate marked the rise to power of the warrior class (samurai) and the gradual suppression of the power of the emperor, who was compelled to govern without effective political or military power, being effectively reduced to a purely symbolical and ceremonial head of state, until the Meiji Restoration over 650 years later." [Wikipedia]