At the time, the U.S. military was so superior to all feasible opponents that it could assume outright domination of an operational area or even a domain of war like the sea, air or land. Today, military thinkers are beginning to realize that total domination might not be attainable or worth the cost under all circumstances. Instead, the application of power should reflect the intensity of American interests in a conflict and the opportunity costs. This means there will be times when the U.S. military will be used to deter or deny an enemy rather than for outright dominance, particularly when the interests involved are modest and the opportunity costs are high.
This type of thinking can be applied to a Syria no-fly zone. As Joseph Holliday of the Institute for the Study of War put it, “a no-fly zone is not a monolithic thing” but a spectrum ranging from expensive and difficult superiority to a gray area where the enemy’s ability to use air power is degraded rather than destroyed. If a few Syrian planes are downed either by land-based missiles or American fighters, then Assad and his generals may cut the number or type of missions they order, or Syrian pilots may find ways to avoid flying assigned missions. This would not be perfect or even decisive, but it could make a difference.
I recommend reading the entire article, Strategic Horizons: For Syria No-Fly Zone, Less Is More, by Steven Metz at World Politics Review.