And since SirH mentioned some war books, I recently had to read Fox of the North for a Russian History class I was taking. It was a biography of General Kutuzov who fought against Napoleon.
It's a very interesting story for me because the concepts that were being implemented by the generals in the days of Napoleon are still proving to be true today. They knew then concepts like holding ground did not win you wars - preservation of your army and destruction of the enemy army did. For 50 years though, we've thought as long as we hold land (or in some cases, just keep retaking land) then somehow the enemy would give up and we'd win. It was fascinating to read this and think, "Duh".