There are several theories why Masayuki and Nobushige dared to side with the Western Camp while the daimyo in Shinano Province all sided with the Eastern Camp, and it is said that the matrimonial relation Masayuki and his son Nobushige had (Masayuki's fifth daughter married into the Uda clan, which is the family home of the wife of Mitsunari ISHIDA, Masayuki's second son Nobushige, being associated with Mitsunari, married with a daughter of Yoshitsugu OTANI who sided with the Western Camp) had a significant influence on their choices.
信濃国の大名がこぞって東軍に与するなか、あえて昌幸と信繁が西軍に与した理由は諸説あるが、昌幸の五女が石田三成の妻の実家である宇田氏に嫁いでおり、しかも昌幸二男信繁も三成と親交があり西軍に与した大谷吉継の娘を妻にしているという姻戚関係が、昌幸・信繁父子の選択に重要な影響を及ぼしたと言われている。