Lying between Pennsylvania and Maryland, which imaginary line came to divide the slave states from the free states in pre Civil War America?

Introduction / Context:
In United States history, certain boundary lines have taken on symbolic meanings that go far beyond geography. One such line, surveyed in the eighteenth century to settle a colonial border dispute, later became famous as the division between slave states and free states before the American Civil War. This question asks you to identify that line, which runs between Pennsylvania and Maryland and is known by the names of the surveyors who measured it.

Given Data / Assumptions:
• The line is imaginary in the sense that it is a surveyed political border, not a natural feature. • It lies between Pennsylvania and Maryland. • In the pre Civil War period, it was seen as a dividing line between slave states and free states. • Options list the Greenwich Meridian, Tropic of Cancer, Mason Dixon Line, International Date Line, and Missouri Compromise Line.

Concept / Approach:
The boundary in question is the Mason Dixon Line, named after English surveyors Charles Mason and Jeremiah Dixon. They surveyed the border between Pennsylvania and Maryland in the eighteenth century to resolve disputes between colonial proprietors. By the early nineteenth century, this line, along with the Ohio River, came to symbolise the separation between northern free states and southern slave states. When exam questions mention Pennsylvania, Maryland, and the division between free and slave territory, they are referring to the Mason Dixon Line, not to astronomical lines like the Greenwich Meridian or Tropic of Cancer.

Step-by-Step Solution:
Step 1: Note the geographical clue that the line is between Pennsylvania and Maryland. Step 2: Recall that the Mason Dixon Line was surveyed to fix that very border. Step 3: Remember its later symbolic role as a boundary between slavery and freedom in the United States. Step 4: Examine the options and identify Mason Dixon Line as the only one that fits both the place and the historical role. Step 5: Select Mason Dixon Line as the correct answer.

Verification / Alternative check:
Standard references on United States history and geography describe the Mason Dixon Line as the demarcation between Maryland and Pennsylvania. They further explain that during the debates over the Missouri Compromise and in the run up to the Civil War, this line came to represent the division between the North and the South, and between slave and free states, along with the Ohio River. These sources consistently associate this line with the names Mason and Dixon and with the Pennsylvania Maryland border, which confirms that the Mason Dixon Line is the correct choice.

Why Other Options Are Wrong:
• The Greenwich Meridian is the prime meridian at zero degrees longitude, passing through Greenwich in London, and has no special connection to American slavery debates. • The Tropic of Cancer is a line of latitude about 23 and a half degrees north of the equator and does not mark political boundaries in the United States. • The International Date Line is an approximate line near 180 degrees longitude used to define calendar dates, not a boundary between states. • The Missouri Compromise Line refers to a legislative boundary at a specific latitude for deciding the status of new territories, but it is not the surveyed border between Pennsylvania and Maryland mentioned in the question.

Common Pitfalls:
• Confusing the Mason Dixon Line with the Missouri Compromise Line because both relate to slavery and regional divisions. • Treating any well known line such as the Tropic of Cancer or the International Date Line as a possible answer without checking the geographic location. • Forgetting that the Mason Dixon Line originally solved a colonial border dispute before gaining its symbolic meaning.

Final Answer:
The imaginary line between Pennsylvania and Maryland that came to divide slave states from free states in pre Civil War America is the Mason Dixon Line.