Respuesta :
A book containing the letters of a US senator during the war, would be a primary source and reliable (as long as the letters have not been edited or abridged or anything), which would be best for a research paper.
Answer:
If my teacher assigned me a research paper on political changes in the United States during the Civil War, I would research a textbook chapter discussing Abraham Lincoln's presidency, as he was the president of the United States during the entire war, and his policies led the nation in the conflict. In addition, one of the main causes of the conflict was the election of Abraham Lincoln itself, which was the event that triggered the secession of the states of the south of the nation.