That´s right, guo is country.
De Guo = Germany
Fa Guo = France
Ying Guo = England
Mei Guo = America
You see the pattern of imitating the country´s pronunciation in a single syllable and putting a guo behind it.
P.S.: España and Spain are in fact very similar: bear in mind Spaniards cannot start words with sp or st, they add an e in front of that.
Another P.S.: Ni Hon means literally "Sun, rising behind a tree" or "tree behind which the sun is rising" - hence the Land of the Rising Sun and the flag.