I am reading "The Dictators" about Hitler and Stalin's lives and paths to power. However, I find it very difficult to follow, because after every page, I must stop and look for some concepts on wikipedia before continuing, like tsarist war, communism, fascism, the allies and their interests. Most of my previous knowledge on WWII comes from movies, but it's very sparse/ scattered tough, and I still don't fully understand the purposes of war. Should I first study some geography and economy? I'd appreciate any tips and recommendations, if possible, in a structured/ chronological way.
For me I had lots of trouble with WWII (and in fact most wars), due to the way history tends to be taught as a jumbled set of disjointed facts and incidents, rather than a coherent story.
So for me at least, the best way to start to make some sense of WWII is to first learn from a good chronological-based narrative-style source. Preferably one with maps. The New Penguin Atlas of Recent History is one good such resource (also covering WWI and the Cold War). For the Pacific theater, the Penguin Historical Atlas of the Pacific is also a great resource. Despite the scope spanning human history, I remember nearly half the maps covering that exact war.
Once you've got the basic chronology in your head, drilling down to specific things without getting totally lost is far easier. Different people learn different ways though. This is just what made things start to click for me.