re: I feel like schools need to start teaching the start of World War II as July 7, 1937...

There is something to your point in that a major violent conflict was happening in Asia prior to the accepted date when WW2 began.

It is hard to determine when a war begins because most of them are echoes of unresolved issues lingering after earlier conflicts or they are trends of the past which have not been soundly altered by better international expectations.

But there are event markers which help us out. Germany invading Poland is a glaring example. Japan's various early adventures in Asia were regional and not yet tied to the global scope. I would reference the earlier Japanese conflicts in a discussion as they are important, but would stay with the traditionally taught dates when Germany invaded Poland as the moment the war became a world war rather than a regional one.

I would also mention the earlier annexations and general belligerence of Germany's National Socialism prior to the outbreak of actual war as these events are important seed events to understand for future reference.

We should study the whole progression and then look at the later conflicts which followed WW2 where the "enemies of my enemies" demonstrated that they were far from friends when they were helping each other fight. They almost immediately began snarling at each other following their "friendship". Actually, they were posturing even before WW2 ended. This new conflict went on for decades.

Lots of lessons which I think were not learned since we often train and arm enemies of our enemies and see them against us in the future.

Some people never learn.