"The chief of Donald's clan could not have struck him with impunity, and for a Southron to so venture—hate entered the young Highlander's blood like a black river and filled his dreams with crimson nightmares."
—Lord of Samarcand
Southron
(ˈsʌðrən)
n
1. chiefly Scot a Southerner, esp an Englishman
2. (Languages) Scot the English language as spoken in England
3. (Historical Terms) dialect chiefly Southern US an inhabitant of the South, esp at the time of the Civil War
adj
(Placename) chiefly Scot of or relating to the South or to England
[Middle English, variant of southerne, southern; see southern.]
Parts of GRRM's Song of Ice and Fire use the phrase as well. GRRM is known for his homages, so it's safe to assume he picked this one up as well.