I have partitioned the independent countries of the world into two groups based on a certain property X that is shared by some countries, but not by the remaining ones. Property X is purely geographic.
The following countries all have this enigmatic property X:
Bolivia, Colombia, Cuba, Libya, Mali, Nicaragua, North-Korea, Portugal, Russia, Senegal, South-Korea, Switzerland, Tajikistan
The following countries do not have the enigmatic property X:
Afghanistan, Argentina, Australia, Austria, Canada, China, Ireland, Jamaica, Lithuania, Oman, Poland, Sudan, Tanzania
What criterion did I use for my enigmatic partition?
Do Brazil, Chad, Denmark, the USA and/or Yemen have this enigmatic property X?
Property X is purely geographic. It can be solved by studying a map of the world.