Loved this movie. One of my absolute favorites. Assuming the King Kong/Godzilla references can be traced back to Totenkopf's experiments the POD would likely be his birth, with the timelines diverging more radically when the German Empire establishes a secret science unit to build superweapons during the Great War. The fact that it's called World War I (and the film is set in 1939) would lead me to believe there was another major conflict sometime in the 20's or early 30's. My money would be some sort of major escalation of the Spanish Civil War. This would inflame Totenkopf's pessimism, driving the plan he sets into motion in the movie.