The Manchukuo Imperial Army was the ground force of the military of the Manchukuo, a puppet state established by Imperial Japan in Manchuria, a region of northeastern China. The force was primarily used for fighting against Communist and Nationalist guerrillas in Manchukuo but also took part in battle against the Soviet Red Army on several occasions. It initially consisted of former National Revolutionary Army troops of the "Young Marshal" Zhang Xueliang who were recruited after the Japanese invasion of Manchuria en masse, but eventually expanded to include new volunteers and conscripts. The Imperial Army increased in size from about 111,000 troops in 1933 to an estimated strength of between 170,000 and 220,000 soldiers at its peak in 1945, being composed of Han Chinese, Manchus, Mongols, Koreans, Japanese, and White Russians. Throughout its existence the majority of its troops were considered to be mostly unreliable by their Japanese officers and advisers, due to poor training and low morale.