What was the connection between the gadsden purchase and the southern railroad route?

The Gadsden Purchase was a transaction that followed the conquest of much of northern Mexico by the United States. Its relationship to the transcontinental railroad is that  it was purchased because it was the most practical route  for the transcontinental railroad.  The purchase was negotiated by the U.S. minister to Mexico, James Gadsden.

the answer is selfishly. hope this !

it was the new england colonies.

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