Why Were the South and West Sometimes Referred to as the Gun

Why were the South and West sometimes referred to as the Gun Belt?

A) The incidence of violent crime there had increased along with the population.
B) The regions had captured the lion's share of Cold War spending.
C) Most of the major small arms manufacturers in the nation had shifted their operations to the regions.
D) None of the states in those regions required that civilians have a license to carry firearms.