It should be noted that many samurai forces that were active throughout this period were not deployed to Korea; most importantly, the daimyo Tokugawa Ieyasu carefully kept forces under his command out of the Korean campaigns, and other samurai commanders who were opposed to Hideyoshi's domination of Japan either mulled Hideyoshi's call to invade Korea or contributed a small token force. Most commanders who did opposed or otherwise resisted/resented Hideyoshi ended up as part of the so-called Eastern Army, while commanders loyal to Hideyoshi and his son (a notable exception to this trend was Katō Kiyomasa, who deployed with Tokugawa and the Eastern Army) were largely committed to the Western Army; the two opposing sides (so named for the relative geographical locations of their respective commanders' domains) would later clash, most notably at the Battle of Sekigahara, which was won by Tokugawa Ieyasu and the Eastern Forces, paving the way for the establishment of the Tokugawa Shogunate.
What force were most commanders opposed to the Korea invasion part of?
Eastern Army