Complex sentence: In 1933 Berlin, Professor Nichols (Smith) runs the American Colony School, which is next door to the Horst Wessel School, where young Germans are indoctrinated in Nazism.
Split into simpler sentences: In 1933 Berlin, Professor Nichols (Smith) runs the American Colony School. It is next to the Horst Wessel School, where young Germans are indoctrinated in Nazism.