WHAT is that characteristic capability or sources of power from which a military force derives its freedom of action physical strength or will to fight?

Oh honey, that's an easy one. It's called "combat power." It's basically the military's ability to kick some serious butt, whether it's through physical strength, technology, strategy, or sheer determination. So, in simpler terms, it's what gives them the mojo to get the job done and come out on top.