The oldest anime I ever watched, back then it was mostly doing whatever Disney or Fleischer were doing but with a Japanese setting (I know it's more complex than that but whatever). In this case it's a short about Mickey Mouse invading an island and the natives fighting against the foreign invader. Despite my love for disney hate, I gotta share what user Systemhalodark said in the comment section of the video:
"The irony, considering that this is what they were doing to China at the same time."
This is from a period before the concept of anime was created, which happened somewhere in the 1960s or 1970s, so it's kinda even hard to think of it in "anime" terms. It's really just a simple animation (I'm writing this just to fill the review length quota)