In Volume 11 of "Nihon Gaishi (historical book on Japan)," which was one of the bestsellers in the Edo Period, it is described as "Later in sengoku (period of warring states), such military forces were divided and owned by local barons (snip) after teaching them, Takeda and Uesugi became the best fighters.
江戸時代にベストセラーとなった『日本外史』でも、巻十一に「降りて戦国に至り、この兵各々群雄の分ち領する所となり(中略)之に教へて後戦う者は、武田・上杉より過ぐるはなし。