The southern Colony
Mexico is the southern neighbor of the U.S.
USA is the closest southern neighbor of Canada.
The closest southern neighbor would be Mexico.
Egypt.
South African Republic (SAR) is Botswana's southern neighbor. http://www.mapsnworld.com/world-map-political.html
Mexico is the southern neighbor of the U.S.
armenia
Panjab
Mexico
Mexico
If the question means USA for America then Mexico is on the southern border of the USA.