In order to stop Russian aggression on Manchuria, Japan invaded Manchuria on 18 September 1939. This was called the Manchurian Crisis (also called the '918 Incident').

为了阻止苏联进佔满洲，日本最终于1939年9月18日入侵满洲，这就是「满洲事件」（又称「九一八事件」）。

youdao

Today, September 18, the anniversary of the 1931 Mukden Incident, was expected to witness another surge of anti-Japanese demonstrations.

FORBES: An Afternoon Observing Anti-Japanese Demonstrations in Shanghai and Thinking "Whither Japan"