We know about the Zimmerman Note and Mexico. Did Germany promise Japan anything for possible support in WWI?

Answer 1

Japan had declared war on Germany in 1914 almost immediately after the beginning of hostilities. Germany's Pacific posessions were too isolated and too strategic for Japan to resist plucking them right up.

Answer 2

Japan was an Ally in WWI. I don't think the Germans even considered their existence.

Answer 3

I doubt Germany would cede all that land to Mexico should they win the war. It sounds like an empty promise.