Johnson first became intimately involved in shaping American policy toward China in 1925 when he assumed the office of Chief of the Division of Far Eastern Affairs in the State Department. In 1929 he came to China as the U.S. Minister to China. His title was Minister, rather than Ambassador, because the U.S. Legation in China had not been raised to the status of an embassy. When in May 1935 Japan said that it planned to raise its Legation in China to the grade of embassy the U.S. moved to follow suit. Due to the required Senate confirmation Johnson did not officially become U.S. ambassador to China until mid-September 1935. Both as Minister and as Ambassador to China, Johnson provided the State Department with important communications that assisted the Coolidge, Hoover, and Roosevelt administrations determine their policies with respect to China and China's unsettled relationship with Japan and the Western powers. For example, during Japan's invasion of Manchuria, which began on the evening of September 18, 1931 near Mukden, Johnson urged Hoover's Secretary of State, Stimson to avoid any appearance of siding with Japan, and to rather uphold the Nine-Power Treaty, which affirmed China's sovereignty. Far Eastern expert Dorothy Borg wrote, "Johnson's cable made a deep impression on Stimson..."