 Since 1931, Japan had been provoking numerous incidents and violating Chinese sovereignty.The Tanggu Truce established a demilitarized zone between Japanese-occupied territories and North China in 1933, but conflict continued unabated via proxy armies in Inner Mongolia.However, with the appointment of Kōki Hirota as Foreign Minister of Japan, the Japanese civilian government attempted to improve Sino-Japanese relations, and on 22 January 1935, Japan announced a policy of nonaggression against China.