Having lost most of China's economic and industrial centers, Chiang withdrew into the hinterlands, stretching the Japanese supply lines and bogging down Japanese soldiers in the vast Chinese interior. As part of a policy of protracted resistance, Chiang authorized the use of scorched earth tactics, resulting in many civilian deaths. During the Nationalists' retreat from Zhengzhou, the dams around the city were deliberately destroyed by the Nationalist army in order to delay the Japanese advance, killing 500,000 people in the subsequent 1938 Yellow River flood.