Hello. You did not quote the text to which this question refers, but I believe you are referring to James McPherson and the work he wrote called "What They Fought." However, you have not specified which part of the text the question refers to, which may leave the textual evidence inaccurate, but I hope I can help you.
In writing "What They Fought" James McPherson aimed to show the reasons that led southern and northern soldiers to maintain the American civil war, especially southern soldiers while they saw the impending defeat. He did this by analyzing letters and diaries of these soldiers who showed their thoughts without any kind of censorship or control. This objective is shown in a very clear and attractive way to the public, primarily because McPerson presents an accessible, easy and direct language text, which allows the reader to quench curiosity about the soldiers' thoughts in the face of such a great conflict.