Already controlling the area along the South Manchuria Railroad, Japan's Kwantung Army further invaded Manchuria (Northeast China) in 1931, following the Mukden Incident, in where Japan claimed to have had territory attacked by the Chinese. By 1937, Japan had annexed territory north of Beijing and, following the Marco Polo Bridge Incident, a full-scale invasion of China began. Japanese military superiority over a weak and demoralized Chinese Republican army allowed for swift advances down the eastern coast, leading to the fall of Shanghai and Nanjing (Nanking, then capital of the Republic of China) the same year. The Chinese suffered greatly in both military and civilian casualties. An estimated 300,000 civilians were killed during the first weeks of Japanese occupation of Nanjing, during the Nanking Massacre.