In June 1935, four Japanese soldiers entered the Zhangbei District of Chahar province, north of the Great Wall, on a journey to Kalgan (Zhangjiakou) and Beiping.
They were detained because they did not have required travel permits from the Chahar Provincial Government.
The Army commander ordered their release, allowing them to continue on their journey, but with the warning that appropriate permits must be obtained in future.
Soon after, the Consul passed along the matter to the Kwantung Army saying it was very grave and was beyond his power to resolve.
You can help Wikipedia by expanding it.This article related to the history of China is a stub.