1. Think of the subject you want to look for. Let's say "Tang Dynasty Military Strategy"
2. Go to wikipedia, look for the article on the period you're looking for. This led me to https://en.wikipedia.org/wiki/Military_history_of_China_before_1911#Sui-Tang
3. Look at the sources and google around a bit.
The nature of history books is a tradeoff between detail and scope. If you have a large scope ("The Roman Empire"), you'll have little detail. If you have a very specific scope ("Appius Claudius Caecus's work on Roman Aqueducts") you can find much more detailed information.
I can't give you any recommendations on books until you disclose what sort of periods you are interested in, but I hope you understand that there is incomprehensible amounts of knowledge out there, and you have to be very specific about what you are looking for.