Additionally. International law operates heavily on precedent, such that in the absence of formal agreements The Way Things Are Done among other nations often has the force of law and can be enforced on those who transgress it.

Now consider the London Blitz, during WWII. Bombing civilian areas with massive damage and loss of life. After the war, Germany wasn't permitted to have any air force at all from 1946 - 1956 (shortly after they joined NATO). That arguably creates the precedent that "if you bomb civilians, other countries can take your air force away". What is Qadaafi doing? Bombing civilians. What do other countries do? Destroy his air force, without involving ground troops.