Anti-communist writers Jung Chang and Jon Halliday assert in their highly controversial 2006 book Mao: The Unknown Story that the Nationalist general Zhang Zhizhong was a Soviet agent who, following the Marco Polo Bridge incident in July 1937, had been tasked by Stalin with escalating the already tense situation with Japan into a full-scale, all-out war.
Stalin ordered this, Chang and Halliday maintain, because he (quite reasonably) feared Japanese aggression against his own country and wanted to draw China and Japan (both of which were hostile towards the USSR) into a costly war with one-another in order to weaken them both. This certainly was the approach he took towards Germany in 1939 after the failure of collective security, so it's not without precedent (or postedent?). In addition, Zhang himself was a strong communist sympathiser who would later defect to Mao's side during the Civil War and serve in his government.
According to Chang and Halliday, Zhang deliberately escalated the situation by orchestrating the Ōyama incident (the killing of two Japanese soldiers in Shanghai) and spreading misinformation to the media about the Japanese attacking the city. This was done in order to pressure Chiang into giving him the greenlight to attack the Japanese garrison there, as Chiang wasn't nearly as gung ho about the whole idea.
The ensuing battle, in which over 700,000 Chinese troops faced off against 300,000 Japanese, saw the decimation of Chiang's army. It resulted in the loss of hundreds of thousands of lives (including Chiang's most elite German-trained troops) and the capture of both Shanghai and eventually Nanking.
What do you think? Is this some crazy crackpot idea invented to demonise Stalin, Mao, and communism as a whole; or might it have some basis in reality?