As a general piece of advice, you may want to take a look at our recent series "Finding and Understanding Sources", which is broadly aimed at undergraduates, and also our Book and Resources List.

Evolution in tactics, strategy or technology? Really depends on what kind of evolution, and where geographically you're situating yourself. A history of warfare by John keegan, and also his other two well known works, face of battle and mask of command, give comparisons and contrasts in technologies and tactics in general. You could also go with Max boot's invisible armies. Victor Davis Hanson is pretty controversial due to his pro-bush views and commentary on the US' current and near current wars, but his carnage and culture compares the 'western' and 'eastern' or just simply non western evolution of strategy and extrapolates that to explain the ascendancy of European and American military hegemony over the past few centuries.

I'll add a couple from what I know. You might want to check out R.A. Brown's English Castles and as a sort of counter-point John Goodall's The English Castle. They'll both discuss the development of the castle from a militaristic stand point but Goodall is very good at elucidating the other components behind changes i.e. changes are not always militaristic-ally driven. And to that point Charles Coulson's Castles in Medieval Society is also very good. For finding more sources - I find that bibliographies are an excellent source of additional readings, especially if something you're interested in comes with a footnote, go check that source out, it might even be more useful than what you're currently reading. Hope this helps in some way.