Can't you make Danzig a free state instead of League of Nations protectorate?
Until 1939, when Germany invaded Poland, Danzig was under nominal control of the League of Nations. The name "Free City" is misleading; Danzig never was truly autonomous during this time, and (as the game depicts with Polish troops in Danzig's borders) it was in reality controlled and used by Poland.
It's among the awkward decisions made at Paris that eventually led to World War II...