So I've been listening to a lot of the album Carolus Rex by Sabaton and playing some Mount and Blade: With Fire and Sword, and this has really sparked my interest in that time period; especially the Swedish Empire, the Russian Empire, as well as later on with the German Empire. Any good book recommendations that are preferably on Amazon and are relatively easy reads for someone who isn't an expert on any of this?
Ah, Sabaton is great.
This era is at the edge of my knowledge, unfortunately. As far as the Thirty Years' War go, you probably can't do better than to start with Peter Wilson, The Thirty Years' War: Europe's Tragedy.
If you're interested in the centuries and developments leading up to the 30YW, I could recommend a few others, but I would still start with Wilson.
You might also want to consider posting this request in one of the daily sticky threads--Theory Thursday, Friday Free-for-All, and Saturday Reading & Research are popular places to request and receive book recommendations. :)
I'd recommend Wars in the Age of Louis XIV: An Encyclopedia of Global Warfare and Civilization to get acquainted the the period generally, as well as The Art of Warfare in the Age of Marlborough.
The Thirty Years War by C. V. Wedgwood and Anthony Grafton is one of my favorites in addition to others already mentioned.
I also recommend Wallenstein: The Enigma of the Thirty Years War by Geoff Mortimer (who has other extensive writing on the time period) which was a case study on Wallenstein who once was a Prince and military leader/commander in chief of the Holy Roman Empire, that was later accused of planning to defect to the Swedes and eventually assassinated. He goes into detail about the war and that time period while focusing on his story and provides a great narrative.