Which primary source document could a historian understand why the us civil war started?

Any document that was written during the event by someone who witnessed the event, such as a document on the Battle of Gettysburg, a primary source document would be by someone who was at the battle, and could see what was happening first hand.

On april 20, 1814, the dethroned emperor left france for the isle of  elba, where he was exiled under the terms of the treaty of fontainebleau.napoleon  would be allowed to ruleelba, which had 12,000 inhabitants. perhaps cruelly, the treaty allowed him to retain the title "emperor."

C. the delegated powers