The G nation is referred to "Gangsta" or "Gangster" nation. The phrase is mainly used for the case of southern cities in U.S. where most African-American people reside, and of course the amount of criminals are truly high. An example city is Compton.
Ice Cube (an American rapper lyrically says): Consider this an invitation to my G nation.
by Sina.B. May 25, 2008