They thought this would preserve strength for an anticipated showdown with the Soviet Union, but by now the Japanese government and GHQ had effectively lost control of the Japanese army in China. With many victories achieved, Japanese field generals escalated the war in Jiangsu in an attempt to wipe out Chinese resistance, but were defeated at the Battle of Taierzhuang (March–April 1938). Afterwards the IJA changed its strategy and deployed almost all of its existing armies in China to attack the city of Wuhan, which had become the political, economic and military center of rump China, in hopes of destroying the fighting strength of the NRA and of forcing the KMT government to negotiate for peace. On June 6, they captured Kaifeng, the capital of Henan, and threatened to take Zhengzhou, the junction of the Pinghan and Longhai railways. To prevent Japanese advances in western and southern China, Chiang Kai-shek, at the suggestion of Chen Guofu, ordered the opening of the dikes on the Yellow River near Zhengzhou. The original plan was to destroy the dike in Zhaokou, but due to difficulties in that place, the Huayuankou dike on the south bank was destroyed on June 5 and June 7 by excavation, with flood waters over eastern Henan, central Anhui, and north central Jiangsu. The floods covered and destroyed thousands of square kilometers of agricultural land and displaced the mouth of the Yellow River hundreds of miles to the south. Thousands of villages were flooded or destroyed and several million villagers were force to evacuate from their homes. 400,000 people including Japanese soldiers drowned and an additional 10 million became refugees. Rivers were filled with corpses as Tanka boat dwellers drowned from boat capsize. Damage to plantations also affected the population which generated later hunger. Despite this, the Japanese captured Wuhan on October 27, 1938, forcing the KMT to retreat to Chongqing (Chungking), but Chiang Kai-shek still refused to negotiate, saying he would only consider talks if Japan agreed to withdraw to the pre-1937 borders. In 1937, the Japanese Imperial Army quickly marched into the heart of Chinese territory. With Japanese casualties and costs mounting, the Imperial General Headquarters attempted to break Chinese resistance by ordering the air branches of their navy and army to launch the war's first massive air raids on civilian targets. Japanese raiders hit the Kuomintang's newly established provisional capital of Chongqing and most other major cities in unoccupied China, leaving many people either dead, injured, or homeless.