Within this time-frame, there was one major flashpoint where war with Japan was narrowly averted. This was in December 1937, when Japanese bombers sank the gunboat USS Panay, and damaged two others, HMS Bee and Ladybird near Nanking. For the first time since World War I, the United States and Great Britain began coordinating a joint diplomatic and military response; and Japan, recognizing it could not fight both nations apologized and paid reparations.
The primary reason war was averted was President Franklin D Roosevelt acted decisively to suppress information about the USS Panay attack. Three journalists recorded the attack. Norman Soong of the New York Times shot 75 photographs of the attack; Eric Meyell of Fox Movietone and Norman Alley of Universal shot well over 70 rolls of film of the attack. The evidence was clear, Japanese warplanes dived as close as 100 feet from the clearly marked USS Panay; the attack was deliberate. Roosevelt personally ensured the most damaging evidence was censored.
There were numerous opportunities for this film evidence to come to light prior to Roosevelt obtaining control over it. This would have substantially expanded the sense of American outrage over the attack. Especially damaging would be the exposure of the Japanese Foreign Ministry's explanations of the attack as an accident to be naked lies. Nor were Japanese naval and military officers on the scene disposed to admitting fault, much less making an apology. The Japanese could well have come to the conclusion that any American and British response would be feeble. Such contempt could well feed an Anglo-American belief the Japanese needed to be reined in, with further escalatory steps towards war. Although certainly not a popular war, and isolationism strong in America, it is possible for the US Congress to declare war on principle only. The case for war against Germany in 1917 was considerably weaker.
I am convinced the the Americans would not go it alone, if the British backed out, they would likely fold. But the British had even greater commercial interests in China, and resented the brusque treatment given them by the Japanese. It would have to be a delicate sequence of events, but combinations of American indignation, Japanese contempt and British belief the Japanese were not playing cricket could have fed the tides towards war.