Though he did well, Terumoto was often criticized by Mori Motonari, who helped raise him, for lacking knowledge and perseverance, seeing as Terumoto had grown without want in the lap of Mori luxury. In a way, this was true: he rode on the foundation which Motonari had created, in addition receiving considerable political and military from the "Two Rivers" Kobayakawa and Kikkawa.
Following his defeat to Hideyoshi in 1582, he was able to retain much of his holdings, partly because Hideyoshi was in a hurry to rush to avenge his slain master, Oda Nobunaga. This submission to Hideyoshi would have major consequences for Terumoto, who would send his troops to both Shikoku and Kyushu to help attack the Chosokabe and Shimazu, respectively. Hideyoshi would not forget his contribution, and in addition to granting Terumoto generous land claims, would manifest his trust by granting him the title of Tairo.
Things were to change following Hideyoshi's death, however. Once the time of battle was nigh, Mori Terumoto became the nominal commander-in-chief of the western army after being persuaded by his advisor Ankokuji Ekei, and Ishida Mitsunari. Despite this, he was made to stay in Osaka castle for the duration of the campaign so as not to create an unbalance of power with the de facto ruler: Ishida Mitsunari.
Following the western army's defeat, Mori withdrew from Osaka castle on September 23, 1600, and was chastised by Ieyasu for not only choosing the wrong side to be fighting on, but also for not fighting during the battle! As a result of this judgment, the fortunes of the Mori clan, which were well in excess of 1 million koku, were to be reduced to less than a third of their original size.
Though the Mori clan would continue to survive, its moment of glory had already passed by the time Sekigahara was over.