What was the political impact of the transcontinental railroad?

It was the plans for building this railroad that divided the nation.

The North wanted it to go via Chicago, the South wanted it to go via New Mexico.

To get the South to agree the Chicago route, Congress had to appease them with the Kansas-Nebraska Act - holding a local vote on slavery, and allowing the possibility of new slave-states.

When the railroad was comeplete, travel across long distances became cheaper and the settlement of the far West was made possible in a much shorter amount of time.