I posed this question to the community at Quora and got some pretty fantastic answers:
From Ian McCullough
Some educated guesses:
1. The Civil War (known in some parts as “The War of Northern Aggression”) created a unified sense of “Southernness” across a very large geographic area. If you mistakenly imply that a person from Mississippi is from Georgia, you’ll get laughed at then politely corrected. If you mistakenly imply that someone from New York is from New Jersey, you run a risk of a fist fight.
2. Expanding on the geographic point, the Southern experience is in many ways a rural experience and an agricultural experience. The vast majority of land in the United States is used for farming and ranching activities.
3. There are only two other American cultural forces that are remotely comparable at this time: Latino and Hip-Hop.
Any East Coast urban-specific cultures are too niche. Although I’m a proud son of the Midwest, we’re the cultural equivalent of beige. West Coast culture – be it LA, SF, or Seattle – is too focused on self-actualizaton to be a binding force. That leaves Native American, Asian, Hawaiian, Alaskan…and maybe surfers. There are mainly numbers issues there. (Although don’t screw around with surfers.)
Hope this informs some thinking until a more eminent scholar can weigh in.
From Kevin Weaver:
For hundreds of years, there was no “broader American culture” but that of the North and South east of the Mississippi. The majority of African Americans, up north and out west, have ancestors who migrated out of the South less than 100 years ago – and many only 1 generation ago. African American culture is the petri dish out of which most mainstream American popular culture grows. African American culture is, by and large, Southern culture.
White Southerners have also heavily influenced American culture. The western states, particularly Southern California, were flooded with Southern whites at the beginning of the 20th century escaping ecological and economic catastrophe. “Okies” and “Arkies” settled in places like Bakersfield, Orange County, and Los Angeles County. Both Rock-and-Roll and Country music are the products of both Southern whites and blacks. Soul music, gospel and jazz are the products of Southern black people who migrated to Detroit and Harlem during the Great Migration.
Religion continues to be tied into the Southern identity; first and foremost, Evangelicalism. Evangelicals are one of the most powerful and consistent voting blocs outside of senior citizens. Because of this Southern evangelicals can either make or break an election that has national implications.
The South, for its size, is also an extremely diverse region. What gets lumped in to the phrase “Southern culture” is actually a cultural powerhouse of many different dialects, cuisines, religious beliefs, viewpoints, and regional identities – such as Appalachian, low country, piedmont, geechee, creole, cajun, delta, coastal peoples, etc. The South provides and has provided fertile soil from which the American imagination continues grow.
Because of these reasons, this question would be better asked: Why does Southern culture continue to have such a profound impact on the broader American culture?
For the record: I was born and raised in Western North Carolina. My ancestry in the Appalachian South precedes the Revolutionary War.