[31] On 7 July 1937, the Imperial Japanese Army (IJA) launched a full-scale invasion of China after the Marco Polo Bridge Incident.

The fighting lasted from 13 August to 12 November, with the Chinese suffering major casualties including "70 percent of Chiang Kai-shek's young officers.

With the fall of three major Chinese cities (Beijing, Tianjin, and Shanghai), there was a large number[vague] of refugees fleeing the fighting in addition to the government facilities and war supplies that needed to be transferred to Chongqing.

Reinforcements were thus dispatched to boost forces in the area, which placed a strain on the Japanese peacetime economy, leading Prime Minister Fumimaro Konoe to reassemble his Cabinet in 1938 and to introduce the National Mobilization Law on 5 May that year, which moved Japan into a wartime economic state.

[37] After the Japanese capture of Nanjing, the bulk of the Nationalist government agencies and the military command headquarters were in Wuhan although the capital had been moved to Chongqing.

The First War Zone, located in the west of the Zhengzhou-Xinyang section of the Pinghan Railway, was given the task of stopping the Japanese forces coming from the North China Plain.

Finally, Chinese troops in the Third War Zone, located between Wuhu, Anqing and Nanchang, were given the task to protect the Yuehan Railway.

After the fall of Xuzhou in May 1938, the Japanese planned an extensive invasion of Hankou and the takeover of Wuhan, and intended to destroy the main force of the National Revolutionary Army.

[citation needed] In an attempt to win more time for the preparation of the defense of Wuhan, the Chinese opened up the dikes of the Yellow River in Huayuankou, Zhengzhou on 9 June.

The capture Anqing's airbase enabled Japanese aircraft to assault Jiujiang, a major riverine port and railroad junction one hundred miles upstream.

[47] To prevent a Japanese assault on Jiujiang, the Chinese had built defensive fortifications at Madang, including artillery emplacements, naval mines and bamboo river booms.

[51] It took almost three weeks for the Japanese to clear the waterway around Madang of mines, costing them five minesweepers, two warships and a landing craft full of marines.

[52] After the fall of Madang, there were some two hundred thousand Chinese troops under the dual command of Xue Yue and Zhang Fukui in the Jiujiang-Ruichang area.

Male civilians were indiscriminately executed alongside any POWs who had failed to retreat in time, whilst women and children were raped en masse.

[52] The Japanese Namita detachment moved westward along the river, landed northeast of Ruichang on 10 August, and mounted an assault on the city.

The Chinese 30th and 18th Corps resisted along the Ruichang-Ruoxi Road and the surrounding area, which resulted in a stalemate for more than a month until the Japanese 27th Division captured Ruoxi on 5 October.

They attempted to occupy De'an County and Nanchang, together with the 106th Division, to protect the southern flank of the Japanese Army, which was advancing westward.

In Shandong, 1,000 soldiers under Shi Yousan, who had defected multiple times to rivaling warlord cliques and was then independent, occupied Jinan and held it for a few days.

While those factions were active, the Japanese 6th Division breached the defensive lines of Chinese 31st and 68th Army on 24 July and captured Taihu, Susong, and Huangmei Counties on 3 August.

[52] To capitalize on this natural defense, the Chinese had built massive battlements and fortifications since the end of 1937, with help provided by Soviet advisors and thousands of local laborers.

[58] To overcome the Chinese defenders, the Japanese resorted to deploying large amounts of poison gas, which proved to be their only their only decisive means of achieving victory.

The 10th Division then continued to move westward but met a Chinese counterattack east of Xinyang and was forced to withdraw back to Lushan.

[62] According to Yoshiaki Yoshimi and Seiya Matsuno, Emperor Shōwa authorized by specific orders (rinsanmei) the use of chemical weapons against the Chinese.

[63] During the Battle of Wuhan, Prince Kan'in Kotohito transmitted the emperor's orders to use toxic gas 375 times, from August to October 1938,[64] despite the 1899 Hague Declaration IV, 2 - Declaration on the Use of Projectiles the Object of Which is the Diffusion of Asphyxiating or Deleterious Gases,[65] Article 23 (a) of the 1907 Hague Convention IV - The Laws and Customs of War on Land,[66] and Article 171 of the Versailles Peace Treaty.

According to another memorandum discovered by the historian Yoshiaki Yoshimi, Prince Naruhiko Higashikuni authorized the use of poison gas against the Chinese on 16 August 1938.

[70] Rana Mitter wrote, "Under General Xue Yue, some 100,000 Chinese troops pushed back Japanese forces at Huangmei.

The Battle of Wuhan bought more time for Chinese forces and equipment in Central China to move farther inland to the mountainous fortress of Chongqing and lay the foundation for an extended war of resistance.

Wuhan and Hubei Province now provided the Japanese with new airbases and logistics to support the massive "joint-strike force" terror-bombing campaign against Chongqing and Chengdu under the codename Operation 100.

[73][74] After its fall 1938 victory in the Battle of Wuhan, Japan advanced deep into Communist territory and redeployed 50,000 troops to the Shanxi-Chahar-Hebei Border Region.

The Chinese managed to preserve their strength to continue resisting the weakened IJA, which reduced its capability to respond to rising tensions between Japan and the Soviet Union at the northeastern borders.