 Defeating the Taira clan, Yoritomo became "de facto" ruler of much of Japan and founder of the Kamakura shogunate, an institution destined to last 141 years and to have immense repercussions over the country's history.The Kamakura shogunate era is called by historians the Kamakura period and, although its end is clearly set (Siege of Kamakura (1333)), its beginning is not.Different historians put Kamakura's beginning at a different point in time within a range that goes from the establishment of Yoritomo's first military government in Kamakura (1180) to his elevation to the rank of in 1192.