Chess Strategy contains a lot of principles.
- Tactics, like skewer and pin
- Basic principles, like attack the center
- Better positioning pieces and taking advantage of a position itself.
- and more.
Positional chess is a part of the strategical chess in my opinion, but a book on positional chess goes even deeper. A LOT deeper. You can sacrifice a whole piece and on some rare occasions a rook and a queen to set up a winning position. Positional chess books focus on teaching you how to see the full potential on a position. That is the difference. Tactical chess is a set of principles and tricks. Understanding the potential of a position though makes you evaluate a position better and opens your mind tofor another level of chess play. For instance, imagine you got an opponent king, and a lot of pawns and pieces around that king. You might be able to use opponents pieces as obstacles for their king to escape. It is like judo. Use opponent's strength to weaken them.