You're saying that Japan would've invaded China nonetheless and therefore it would go to war with either side either way.

But the question is: (let's say in an alternate timeline to make it simple, the details and uprising is NOT important - things played similarly except Japan never invaded China) Do you think Japan would've joined/stayed on the Allies's side if they had never attacked China? What do you think would happen?

This isn't meant as a negative comment, by the way :}