Kasugayama Castle was the Uesugi clan's principal mountain stronghold since the days of Uesugi Kenshin, and it was here that Kanetsugu grew up in close attendance on Uesugi Kagekatsu, developing the skills that would define his career. During the Otate no Ran succession war of 1578-79 he helped secure Kagekatsu's victory with the castle as their base, taking his first step toward becoming the clan's chief administrator.

Kasugayama Castle was Kenshin's enduring stronghold, a mountain fortress that exploited the natural terrain to devastating defensive effect. From here the 'Dragon of Echigo' conducted five campaigns against Takeda Shingen and repeated forays into Kanto, earning his reputation as one of the Sengoku era's supreme commanders. The castle remained the Uesugi seat until their transfer to Aizu in 1598.