He was known as an expert on Chinese affairs, had close relationships with leading figures in the Kuomintang (KMT)'s National Revolutionary Army during the 1920s, and expressed sympathy for their cause.

A violent encounter with KMT forces during the 1928 Jinan incident, however, led him to abandon his pro-KMT stance, and adopt a pessimistic attitude toward China.

He later served as chief military advisor to the Japanese puppet state Manchukuo, and during the Second Sino-Japanese War, he was involved in perpetrating the Nanjing massacre.

[1] His family later moved to Hiroshima, where he attended Seibi Primary School, which was affiliated with the Kaikosha, an organisation that provided a number of services to officers of the Imperial Japanese Army.

[3] Sasaki failed to gain admission to the Army War College in December of that year, after the outbreak of the Xinhai Revolution that overthrew the Qing dynasty.

Sasaki wrote in his Autobiography of a Soldier that he received praise for his orchestration of negotiations with revolutionaries in the area, whereby he arranged for their transit through Tieling without conflict.

Having received advice that he would need to graduate the Army War College if he wanted to become a China specialist for the military, Sasaki took the entrance test again in 1914, gaining admission.

He travelled to Nanjing and Hankou (part of what is now Wuhan), and planned to visit Henan Province, but contracted the Spanish flu mid-journey and was forced to call off the expedition to convalesce.

[7] In September 1919, he was assigned to the Siberian Expeditionary Army, and served in the Japanese intervention in Siberia during the Russian Civil War, based in Manzhouli.

Having completed this mission, the unknowing Sasaki reported to the Japanese command in Vladivostok, upon which he was reprimanded for aiding Semyonov, whose presence in the region could upset Japan's efforts to support the Far Eastern Republic neutral buffer state.

[10] Sasaki wrote that this experience affected him greatly, and that he seriously considered quitting the military, but decided to remain following advice from his friend Sakai Takashi, who then worked in the China Department at the Imperial Japanese Army General Staff Office.

[10] In August 1922, Sasaki, now holding the rank of major, was approached about his willingness to replace Isogai Rensuke as Japan's military attaché in Guangzhou, which was the base of Sun Yat-sen's Kuomintang (KMT) government.

[13] In contrast, Sasaki viewed the warlord armies as an anti-societal "collection of beggars, thugs, gamblers, and thieves",[14] and considered them the primary obstacle to China's reunification.

[11] In June 1924, on invitation from Japanese-trained General Instructor He Yingqin, Sasaki visited the newly-opened Whampoa Military Academy, and was struck by its resemblance to his alma mater.

Around this time, an anti-British strike had paralysed the Shamian concession where Sasaki lived, and he expressed his sympathy for the strikers, who he believed were on the path to restoring sovereignty to China.

[18] In November 1924, Sasaki was ordered to return to China to report on the proceedings of a conference between Sun, Beiyang leader Zhang Zuolin, and Duan Qirui in the aftermath of the Second Zhili–Fengtian War.

[21] Continuing to make numerous trips to China, Sasaki was promoted to lieutenant colonel in 1926, and in September of that year, was assigned to the Japanese Legation in Beijing as aide to military attaché Honjō Shigeru.

[22] Sasaki, who still despised the warlords of the Beiyang government, did not get along with their Japanese military advisors, and actively avoided attending banquets held by Zhang Zuolin.

[23] Around this time, Chiang Kai-shek had taken up leadership of the National Revolutionary Army (NRA), begun the Northern Expedition to reunify China, and had attacked Hankou.

[30] Upon the NRA's arrival into Jinan, Sasaki met with the Japanese commander in the city, Major General Saitō Ryū, to convey a message from Chiang Kai-shek.

Sasaki's words were twisted by newspapers into expressing support for the KMT side, and he was treated as a coward and traitor upon his arrival back in Japan.

When Chiang Kai-shek visited the badly injured Sasaki during the Jinan incident, he expressed distrust in the actions of the Japanese military, and said that his hopes for co-operation had evaporated.

[36] Sasaki, who felt betrayed by the KMT, wrote to his superiors that if the Chinese tried to evade responsibility for the Jinan incident, the Japanese would have no choice but to respond with force, now favouring a hard-line approach.

[42] During this time, Sasaki also cultivated a plan to use four cadets who had participated in the 15 May incident coup attempt as agents to promote resistance against European colonial rule in Southeast Asia, though this never came to fruition.

[44] He wrote that he viewed the Mukden incident as a "revolution" that had liberated the people of Manchuria from "feudal" warlord rule, and an attempt to establish a modern "moral state" rooted in multi-ethnic harmony.

If we include those [Chinese] whose escape rafts or boats on the Yangtze were sunk by fire from our armoured cars, plus POWs killed by our units, our detachment alone must have taken care of over 20,000.

However, as one looks upon the sorry state of this destroyed capital, now merely a fading dream of prosperity, there is not a soul who could help but feel deeply emotional.In March 1938, he was elevated to lieutenant general, and served as the commander of the 3rd Independent Mixed Brigade.

[58] Sasaki, who was known for his success in endeavouring to pacify (Japanese: 治安粛正, chian shukusei) Manchukuo, performed a similar role in North China.