I want a better understanding and knowledge of history, but I've noticed I don't retain a lot of information that I read. Should I expect to remember even some portion of a book after a first readthrough? Should I rely on reading other books that have overlapping themes/dates/events? Is there a method that has helped you get better at reading history?
As many of us can probably attest to, reading history books can sometimes be a test of patience. Not everyone who writes a history book is necessarily great at the writing part which can make it hard to push through to the end of a book, much less understand and remember everything they just talked about.
Here are some things that I usually do when I'm reading:
I always make sure that I'm somewhere comfortable. Whether it be your bed or a local coffee shop, you want to be somewhere where you can let your mind relax and not get distracted by other things.
I always take as long as I need to get through the book. Sometimes I can get through a 500 page book in a day and sometimes it takes me a week to get through a 200 page book. The key is that you don't want to rush it. If you haven't understood the first ten pages, pushing onto the next 180 is not going to make things better. In addition to that, if you start to feel tired, take a break. You're likely to remember less if you're reading while tired.
Take notes. I know this makes it sound like homework and takes the fun out of casual reading, but it's definitely one of the most important things you can do for reading comprehension. I prefer doing it by hand in a notebook instead of writing in the book or typing them. Reprocessing the information you just read by writing it down really helps it stick in your brain and it gives you something you can refer back to later when you want to refresh yourself.
Sometimes, when I'm reading a book on a certain time period or geographical region, I really get in the mood and apply the subject to other aspects of my life. For example, one time I was doing some reading for a class on the American West and started watching Westerns and playing Western themed video games, as well, because I was just getting into it. I don't know if it really helps in reading comprehension, but it's fun and can really jazz you up about your readings.
What a great question! Feeling like you don't remember (and therefore don't understand????) parts of a book, or an entire book, can be an isolating experience. Maybe you feel like you're not very smart, or just bad at reading. Happens to everyone. A couple of years ago, I realised that I hardly read at all anymore. I decided to do Goodreads' 52 books challenge, and kept a book journal in which I wrote down which books I read when, and what I thought. Some books I forgot, but a lot of them I remembered.
Now, when it comes to history books, they are quite different from novels. There is a lot of densely packed information, and skill in writing comes second to historical knowledge. What I find helpful is to underline the most important bits (and limiting oneself is really important here), which I can then reskim before reading the next chapter. If the book is very dense or hard to read, I'll try to limit myself to one chapter per session. If not, I might read until I feel like I've had enough.
As /u/RockNRollJedi said, taking notes is immensely helpful, even if it can fee like homework. It's also much more reliable than taking notes in your head!