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..." Johnson made major contributions during the Coolidge, Hoover, and the early Roosevelt administrations. He favored going as far as American interests would allow in helping China regain its sovereignty, and he consistently guided US Secretaries of State Kellogg and Stimson on a moderate course in their policy. Johnson was Frank B. Kellogg's, Coolidge's Secretary of State, principal advisor on China policy. Johnson's recommendations were guided by an instinctive understanding that the rationale for and the time of imperialism was at an end. Consequently, he advocated that the United States and the world powers move toward restoring China's sovereignty as soon as possible. Johnson understood that revolution along with violence and disorder would likely be necessary in bringing about China's development. Kellogg and Johnson hoped that U.S. leadership in the restoration of China's sovereignty would result in retaining China's friendship. Johnson continually opposed interference in the civil war in China. He opposed joining the British at Canton and Hankow in punitive measures against Chinese strikers and other nationalists. He opposed harsh or recriminatory action against China during the Nanking Incident of 1927. He advocated conciliation in answering China's note of June 1925 requesting treaty revision. He suggested going as far as possible, unilaterally if necessary, in writing a new tariff treaty, and he favored gradual relinquishment of extraterritoriality. A new treaty between the United States and China was signed in July 1928 that granted China tariff autonomy and that contained mutual guarantees of most-favored-nation treatment. The treaty marked a milestone that symbolized Kellogg's and Johnson' quest to be China's friend