According to George Bailey Sansom, Nagao Tamekage's career makes him representative of the emergence of the daimyo, and the shift of regional power from the shugo (constables ), governors, and other government officials to independent lords.
He is perhaps best known as the biological father of Nagao Kagetora, who would be adopted into the Uesugi family as Uesugi Kenshin, and would go on to become one of the most famous of all Sengoku period daimyo.
Serving as Deputy (shugo-dai) to Fusayoshi, shugo of Echigo Province, Tamekage led his lord's Yamanouchi Uesugi forces to victory against the Ōgigayatsu Uesugi in a series of conflicts from 1500-1505. However, one of a number of nari-agari mono (成り上がり者), or "upstarts" of this period, Tamekage sought to usurp his lord, and battled with Uesugi forces a number of times in the first decade of the 16th century. He ultimately laid siege to Uesugi Fusayoshi in 1507, at Matsunoyama in Echigo Province, and Fusayoshi was killed. Tamekage then went on to pursue a number of campaigns of his own, gathering territory and power. In 1510, Tamekage plotted with Jinbo Nagakiyo in an attempt to overtake the Jinbo clan from within, using his status as shugo-dai to bring Nagakiyo to his side. Nagakiyo then brought his brother Jinbo Nagatsuna into the plot, which revolved around overthrowing Jinbo Yoshimune and allying with the Uesugi. The plot stretched longer than a year, and Tamekage's patience grew thin. It is believed that Tamekage "arranged" for correspondence between himself and the brothers to be discovered by an ally of Yoshimune, which would lead to their executions, perhaps a quicker route to weakening the Jinbo than the possibly ill-conceived plot with Nagakiyo. The Jinbo brothers were executed, and the Jinbo weakened.
Tamekage then engaged Uesugi Akisada, and defeated him as well, with the help of Hōjō Sōun, another growing power in the region. Within a few years, Nagao and Hōjō brought about the complete collapse of the Uesugi clan.
However, the Senran-ki records him stepping down in favor of his third son and becoming a monk in 1540.
- Abe, Yoshichiro "Sengoku no Kassen Zenroku" (戦国の合戦全録) Japan, 1973