Having a good grasp of geography no doubt makes reading history easier, as you can much easier picture where geographical locations mentioned are actually situated on the map without having to refer back to the map constantly. Also, it makes it easier to appreciate the strategic value of certain geographical locations - especially when you're dealing with power politics, wars and kings.
When I studied for my bachelor's degree a number of years ago, the course's main book for overview was R.R.Palmer and Joel Colton's A History of the Modern World. I have kept this book, and I keep going back to it regularly. Nevertheless, I wish I had paid more attention to some chapters in the book, more specifically to a chapter called "A Few Words on Geography." Let me cite a passage from that chapter:
For most of its history Europe was in fact made up of a diversity of small local units, pockets of territory each having its own customs, way of life, manner of speech, each largely unknown to the others and looking inward upon itself, rather than the blocks called "Germany" or "France" that we take for granted on a map today.
Last year, I read something along those same lines in another book that I bought, The Discovery of France by Graham Robb. Robb is really describing a France where the idea of a French nation wasn't that well rooted everywhere. According to Robb, up until "as late as 1886, over four fifths of the population were still described as 'almost stationary'", and "the sense of identity attached to [the village or regions] was more potent than any later sense of being French."
There is a book about the Italian unification coming out quite soon, The Pursuit of Italy by David Gilmoure, of which I read a review of in the Economist the other day. At the time of the unification process in the 1850s and 60s, the Italians don't seem to have been more closely knit as a nation than the French, and maybe less so. Let me cite a quote I got from the review. In 1861, Massimo d'Azeglio, a pioneer of the unification is supposed to have said, “we have made Italy; now we must make Italians,” implying that the Italians as a nation did not exist.
So, rather than being the nation states made up of subjects with a clear identity of being Italian, French, German, etc, the states at this time were mere regions within where there was one sovereign power. That is, they were an expression of a power relationship. When studying power politics, as I myself tends to find interesting, that is obviously relevant. But in understanding the mentality of people, it would be grossly misleading to think of states in the mentioned period in the sense that we do today.