You are right. The citizens have to see the necessity of a particular war or they will drift back to their own interests as the urgency fades. The longer it goes on, and the less they feel in danger, the more they will question the need to continue. Popular support is probably the major factor, strategy and tactics are the domain of the warriors.
I would add one additional concept...public ownership. Those that feel that they are porotected regardless of the outcome of the military activity do not feel ownership, because they do not feel that they have a dog in the fight. How does one go about making everyone an "owner" of the military action? Those of us who appreciate the fact that American citizens died on 9/11 already feel ownership. But so many untouched by this attack have no interest in addressing the issue, and do not "own" it.