I'd love to get a glimpse into the mind of these people. Especially of those who include keynote interests in a soldier's psychology during war during different time periods, as well as tactics and strategy.
Yes, the papers and diaries of many significant people in history, including generals, have been published. Take a look at this list of projects affiliated with the Association for Documentary Editing--there are about 20 projects listed under "military history." Some projects you'll find online for free like the Papers of George Washington or the Papers of Ulysses S. Grant (look under "search & browse"--unfortunately they use a lousy document viewer), and other projects are subscription based like the Papers of Dwight D. Eisenhower (if you have access to a university library, it's worth checking to see if your institution subscribes). Other projects you might have to get through interlibrary loan through your local library.
Even if you google a general's name and "diary" or "journal" you might have something pertinent pop up. For instance, the Memoirs of Ulysses S. Grant was a massive bestseller back when it was published and it's in the public domain now.