Modern Strategy by Colin S. Gray. Straightforward and readable so far. A useful mainstream foundational primer for the layperson.

The moral of this chapter, perhaps, is that we learn from history both that we cannot learn from history and that human beings continue to be literally capable of anything. The sadness of strategic history that sparks sentimental popular songs with rhetorical lines such as 'when will they ever learn?' promotes the hard-nosed question, 'learn what?' The horror of war has been known to mankind for ever. If full recognition of that horror were all that we humans had to learn, then the social institution of war might have been long banished. Unfortunately, things are not quite that elementally simple. (from Modern Strategy by Colin Gray)
Modern Strategy by Colin Gray - amazon