C to overthrow the government and establish a new one.
The correct answer to this open question is the following.
Although the question is incomplete because it does not provide a specific reference about the author of the letter or any other reference, we can comment on the following.
A primary source is the piece of information that was written by a character or an individual that lived in the moment of the event, was part of the event, or witnessed the event. This individual could have written a letter, or a document -including a book. Or he/she took a photograph. Or was part of an interview. The secondary source includes information from a third person who was not part of the time or event but has found information through other resources. It is the case of an encyclopedia or researchers/historian books.
Answer: in the words of Thanos "a small price to pay for salvation" I mean when the south lost the civil war it allowed the slaves to be set freed if the south would've won there would be slaves to this day