I personally would go with the South, even though I don't live there. Edit: hypothetical leaders of each side: North- Bernie Sanders and Hillary Clinton South- Ted Cruz and Rand Paul Edit2: South would include Texas, South Carolina, North Carolina, Virginia, Tennessee, Kentucky, Kansas, Missouri, Arizona, Georgia, Alabama, Mississippi, Louisiana, Florida, New Mexico, Montana, Wyoming, Nevada, Alaska, Arkansas, and Oklahoma. North is everything else Edit3: the split would be over economics and size of government. Hypothetically a party would attempt a takeover and a conversion of the US to an oppressive form of socialism, causing a split in the union