They are considered the starting point by some historians. The reason it isn't a mainstream view is because frankly the war between china and japan was just that, a war between china and japan. The second- Sino Japanese war was important but it for the most part was between japan and china with some outside clandestine help for the Chinese. The war was for all intensive purposes in its own little bubble.

Well, there is debate in this regard. North America and Europe typically say the war went from 1939-1945. In Asia, the dating is different. Many date the start of the war to 1931 and the Mukden incident. Some historians talk about the Pacific War beginning in 1931. Others date it even earlier, to 1905 when Japan annexed Korea. Others say that we shouldn't separate WWI and WWII into two separate wars since they're so connected. There's a lot of politics tied in with these views, with right and left wings counting differently.