Given you are from the UK I'll assume you are unaware of the significance of the Mason-Dixon line in the US.

From Wikipedia:

In popular usage, the Mason–Dixon line symbolizes a cultural boundary between the North and the South (Dixie). After Pennsylvania abolished slavery, it served as a demarcation line for the legality of slavery. That demarcation did not extend beyond Pennsylvania because Delaware, then a slave state, extended north and east of the boundary. Also lying north and east of the boundary was New Jersey, where slavery was formally abolished in 1846, but former slaves continued to be "apprenticed" to their masters until the passage of the Thirteenth Amendment to the U.S. Constitution in 1865. The Missouri Compromise line had a much clearer geographic connection to slavery in the United States leading up to the Civil War.[24]

More about it can be found at http://en.wikipedia.org/wiki/Mason%E2%80%93Dixon_line or just Google the phrase Mason-Dixon Line.

Even though we sort of share a common language there are numerous cultural differences. Kinda like when I was in Australia and requested a "dime in exchange for two nickles" from a shop keeper. She had no idea as to what I was talking about, but when I changed it to a "ten cent piece for two 5 cent pieces" she understood fully. I later learned those are the proper terms for the Australian coins.