Actually, whatever his real feelings might be, after the ruin of Katsuie, he simply took the tonsure without resistance and bowed before Hideyoshi, and he dispatched only a small troop for the Battle of Shizugatake, which might be due to public position of preparations for the Uesugi clan, it is widely thought that especially after the death of Nobunaga, they tied the relationship due to the interest that they did not want to create enemy each other.
実際、本心はともかく勝家の滅亡後は、あっさり抗戦する事なく剃髪し秀吉に降っていたり、上杉家への備えという建前もあるが、賤ヶ岳の戦いでも僅かな援兵しか派遣していない事などから、ことさら信長死後は、お互い背後に敵を作りたくないという利害関係上、結んでいたという見解が強い。