The Mason -- Dixon line, also called the Mason and Dixon line or Mason's and Dixon's line, was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute involving Maryland, Pennsylvania, and Delaware in Colonial America. It is still a demarcation line among four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and West Virginia (originally part of Virginia before 1863). Later it became known as the border between the North and South. Before the Missouri Compromise, the line (west of Delaware) marked the northern limit of slavery in the United States.

Based on this passage, where does the north begin in the us? Let's think fast. Stream of consciousness:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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To answer the question, consider the following: Later it became known as the border between the North and South. So the final answer is The Mason -- Dixon line.