BACKGROUND In early 1940, troops of the Imperial Japanese Army (IJA) moved to seize Longzhou in south Guangxi, where the eastern branch of the railroad from Hanoi reaches the border, and also tried to move west to cut the rail line to Kunming. Chinese resistance, supplied from Indochina, was tough.
Then on 22 June 1940, France signed an armistice with Germany, Japan's Axis ally. This established the neutral but pro-Axis Vichy France government in the unoccupied part of France. Vichy France also controlled most French overseas possessions, including Indochina.
The IJA captured Longzhou, closing one route, but the rail line to Yunnan was still open. Japanese aerial bombing did not close it.
Japan pressured the Vichy government to close the railway, but the French did not agree.