Q: Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Context : At the eve of World War II, on 1 September 1939, Eugen Muller was assigned to the Headquarters Chief of Staff of the Army, under the command of Generaloberst Franz Halder.
Answer : World War II
A:
In what war was Eugen Muller in?