For the next three years, IJN and ROCAF pilots fought above Beijing, Shanghai, Nanjing, Wuhan and elsewhere as Japan sought unsuccessfully to subdue China. Sometimes IJN carrier air groups were sent temporarily to land bases. Both air forces suffered defeats and enjoyed victories. Losing ground, the Chinese shifted their capital westward and inland until establishing it at Chongqing in central China. By 1941, Japan held large portions of northern and coastal China but had been weakened by the battles for inland central China. In mid-September 1941, as the IJN began to focus on the possibility of a wider war in the Pacific, it turned over responsibility for the air war over China to the IJA. Continued resistance by China's National Revolutionary Army led to a war of attrition that tied down large numbers of Japanese troops until the end of World War II in 1945.