The circle indicate the time we are discussing in this section
Kamakura period was the golden age of sword making. Many valuable swords now exist were made during the Kamakura period. The war between Genii clan and Heike clan in the late Heian period demanded more swords and more swordsmiths.
After the Gen-Pei war (源平 The war between Genji and Heishi), the results of many precious live experiences led to improving in sword making techniques. Also, the Emperor Gotoba encouraged sword making and treated sword smiths very highly. As a result, they created large numbers of valuable swords during the Kamakura period.
The style of the swords during the Kamakura period varies considerably, we usually divide into three stages; early Kamakura period, middle Kamakura period, late Kamakura period.
The Kamakura period was called Kamakura period because the center of the political power that is called Kamakura Bakufu (鎌倉幕府) was established at Kamakura area by Minamoto-no-Yoritomo (源頼朝). He was the head of the Genji clan.
At the end of the Heian period, the Genji and the Heishi were the two major powerful Samurai group. The head of the Genji (源氏) attacked Heike (also called Heishi (平氏), but the Genji failed. As a result, a direct line of Genji, Minamoto-no-Yoritomo (源頼朝) was sent to Izu Island. He was still a child. Izu island was considered very far away then. The Heishi clan became the top of the society. It was said, “if you are not a part of the Heishi family, you are not a human being”. A society like that created too many enemies. Meantime, Yoritomo who were in Izu island grew to be a young man. He met Hojo Masako (北条政子). She was a daughter of a small local official, Hojo Tokimasa in Izu Island. Eventually, Minamoto-no-Yoritomo raised an army, with the help of his wife Masako and Hojo family. Yoritomo, Hojo, and other Genji relations attacked the Heishi clan and won the war, that end the Heian period. The political power and military power shifted to the Kamakura government (鎌倉幕府) in Kamakura.
Yet the imperial court and aristocrats still existed in Kyoto. Kamakura Bakufu had military, police and political power. The imperial court was the department of public administration. Thus, those two big rivals controlled the country in the different field and kept the balance between them.