Kwantung Army

Map of the area in 1921 (Wikipedia).

After the Russo-Japanese war, in 1905, Japan replaced Russia as holder of the Kwantung Leased Territory. One year later, the Kwantung Garrison was created to defend the leased territory, and was renamed to Kwantung Army in 1919, when it had a total strength of 10.000 men.

Kwantung Army was an army group of the Imperial Japanese Army (IJA), and despite being under command of the Imperial General Headquarters, its officers were known for their insubordinate attitude referred as Gekokujō: "overthrowing or surpassing one's superior" or "rule from below".

Map of the area in 1931.

Following Gekokujō doctrine, Kwantung Army officers unilaterally plotted the Mukden Incident: they detonated a small bomb close to a Japanese owned railway line near Mukden. They then blamed Chinese activists for the explosion and invaded the Chinese province of Manchuria, without having any authorization from the General Headquarters.

Due to the success of the invasion, Kwantung Army's insubordination was rewarded instead of punished. They were assigned the defense and the control of the administration of the newly created puppet State of Manchukuo over former Manchurian territory in 1932, as well as the creation and training of the Manchukuo Imperial Army.

Kenkichi Ueda (Wikipedia).

At the time of the Nomonhan Incident in 1939, Kwantung Army had grown to a strength of about 700.000 troops, and its Command was formed by army commander Lieutenant General Kenkichi Ueda, chief of staff Lieutenant General Rensuke Isogai and vice chief of staff General Otozaburo Yano. Army officers wanted to take actions to invade Siberia instead of focusing on China (the second Sino-Japanese war had started in 1937). They were frustrated with Imperial Army Headquarters after the incident of Amur River (1937) and the Battle of Lake Khasan (1938). These were small incidents that occurred at the border with the Soviet Union, caused by soviet incursions into disputed border terrain without clear border lines, and responded with gekokujō actions from Kwantung army officers which were opposed and constrained by the Imperial Headquarters, who did not want these incidents to escalate to large conflicts which could end up in a two-front war for Japan: against China and USSR.

Masanobu Tsuji (Wikipedia)

As a result of the resentment and frustration in the Kwantung Army command, a new set of guidelines for the conduct of its troops in case of border conflict were proposed. These aggressive and tough guides, drafted by Kwantung Army Major Masanobu Tsuji, were called "Principles for the Settlement of Soviet-Manchukuoan Border Disputes" and stated that "If Soviet troops transgress the Manchukuoan frontiers, Kwantung Army will nip their ambitions in the bud by completely destroying them" (Nomonhan, 1939 The Red Army's Victory That Shaped WWII, Stuart D. Goldman).

Despite the guideline being rather provocative and aggressive than cautious towards the Soviet neighbors, Imperial Headquarters approved them on April 25th, because they did not want to increase the tension with Kwantung Army and because they were focused on the war with China.

Just three weeks later, on May 13th, 23th Division Lieutenant General Michitarō Komatsubara was informed that some Mongolian cavalry units had crossed into what he believed to be Manchukuo territory. Following the newly promulgated guideline, he decided to counterattack with strength, starting the Nomonhan Incident.

Kwantung Army Headquarters in Hsinking, Manchukuo (Wikipedia).