Just found this book while browsing on archive.org, I suppose it actually fits in multiple sections of the forum, but I thought this one would be best. I've only read a few pages of it so far, but it seems like an interesting read.
The scout and ranger: being the personal adventures of Corporal Pike, of the Fourth Ohio cavalry. As a Texan ranger, in the Indian wars, delineating western adventure; afterwards a scout and spy, in Tennessee, Alabama, Georgia, and the Carolinas, under General Mitchell, Rosecrans, Stanley, Sheridan, Lytle, Thomas, Crook, and Sherman. Fully illustrating the secret service. Twenty-five full-page engravings (1865)
Read the book online or download it here: https://archive.org/details/scoutrangerbeing00pike