[1] After Japan's victory in the Russo-Japanese War of 1904–1905, and subsequent occupation, and then annexation of Korea in 1910, the need was felt for a dedicated garrison force, raised from people with local knowledge.

However, following the Marco Polo Bridge Incident from 11 July 1937, the division was again dispatched to the north China theater of operations under the command of Lieutenant General Bunzaburō Kawagishi, as part of the 1st army.

[2] From October 1943, the 20th Infantry Division under Lieutenant General Shigemasa Aoki, was transferred to the Japanese Eighteenth Army in the Southern Area Command (New Guinea).

Aoki died of malaria in July 1943, and was replaced by Lieutenant General Shigeru Katagiri, who established his headquarters near Gali, and marched with his troops 200 miles (320 km) to reinforce Finschhafen after the Allied landings at Lae and Nadzab on 4 September 1943.

The surviving forces of the Nakai Detachment of the 20th division held out against the Australian Army in the Markham, Ramu and Finisterre campaigns and other combat operations in New Guinea until the end of the war.