The Tanggu Truce established a demilitarized zone between Japanese-occupied territories and North China in 1933, but conflict continued unabated by 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.
On 29 May 1935, General Takashi Sakai, Chief of Staff of the Japanese China Garrison Army, which was based in Tianjin, acted on the pretext that two pro-Japanese heads of a local news service had been assassinated and raised a formal protest to the Kuomintang General He Yingqin, Acting Chairman of the Peiping National Military Council.
Not prepared at the time to go to war with Japan since his forces were still tied down in a campaign to exterminate the Chinese Communist Party, Chiang Kai-shek agreed to comply.
[3] Although the agreement had been reached in secret, its details were soon leaked to the press, which caused an upsurge in indignation and anti-Japanese sentiment in China.