What course should I use as an international to study US History and World History?

Hello Ian.  An AP class goes into more detail and depth than a regular class.  To get a basic understanding of US History, do the regular US History.  If you feel that you understand all the information easily, do the AP US History.

If you want to go through the whole history of humanity, then do the World History Project Origins, but if you want more details on the world wars than is provided in Project Origins, then do World History 1750.

Also, I do not think Khan Academy has AP World History.

Hope this helps.