The Art of War by Sun Tzu.

I Laying Plans contd....

[The Moral law - number one of the five constant factors to be taken into account in one's deliberations, when seeking to determine the conditions obtaining in the field]

5,6 The Moral Law causes the people to be in complete accord with their ruler, so that they will follow him regardless of their lives, undismayed by any danger.

(Zepyhrist: In other words winning a battle is much easier with the support of your own people and all other things being equal this support would determine the winner. Plus if you do not have the support of the people, should you really be going to war.)