Start by naming any country that France borders. Then name any country that borders any of those countries. Then keep going until there are no more countries left to name.
Imperialism makes this a bit complicated; could do with allowing 'Dutch East Indies' as well as Indonesia for instance, and several others were British colonies at the time.
I wonder how much is affected by it being 1940 - i.e. WWII had started (but not everywhere). It would be interesting to compare this to a list from 1938.