Strategy and Force Planning 2E is a collection of essays, usually republished from other sources, discussing various issues on deciding what a country's (specifically the United States) military force should be structured in the near to mid-term future. The book is published by the Naval War College Press and I found the third edition (2000) and fourth edition (2004) can be read online.

The book is divided into parts, each with several essays.

1. Strategy and Force Planning Concepts
2. Perspectives on International Relations
3. National Interests and Grand Strategy
4. Economic Strategy
5. Diplomatic Strategy
6. Geostrategic Planning
7. Military Strategy and Force Planning
8. The Military in the Future

As you might see from the above, determining an optimal military force structure depends on things like:

What allies do you have to help you? (Part 2)
What are your national priorities? (Part 3)
How can you influence other countries through economic or diplomatic levers? (Parts 4 and 5)
What do you need in power projection to accomplish your goals? (Part 6)
What should be considered 20 to 30 years from now when the nature of war might have a sudden shift? (Part 8)

This is not a book about "these are the answers". This is a book about "what questions do we need to ask" and "what different strategies are possible".

I found this book dense but quite interesting. Even though Second Edition has the Gulf War (1991) as a major example to discuss around I don't feel the book is obsolete. Naturally subsequent editions add and remove articles (at a glance comparing second and fourth edition almost half the articles have been switched out with different ones). But many concepts stay the same.

So overall a worthwhile read.