"Bad cases make bad law." This axiom of jurisprudence can as easily apply to the use of force. What is happening in Libya at the moment is a "bad case" in three ways: military intervention in its civil war does not derive from well-established precedent, does not draw on unambiguous principle, and may not set a course or parameters for future conduct of various nations and institutions in similar — or roughly similar — cases. This conclusion will be tested the next time the U.S., its European and Canadian allies, and others are faced with a situation that seems to cry for outside intervention.
This is not to say that decisions on Libya taken in Paris, London, Washington and other capitals, plus at NATO headquarters in Brussels, came out of nowhere. They were based on a resolution of the UN Security Council (under Chapter VII enforcement provisions of the UN Charter). That has been important in the past to NATO's European members and to some other countries, although not always a necessary condition. Witness the NATO air campaign to stop Slobodan Milosevic's ethnic cleansing in 1999 in Kosovo. (In that situation, in the absence of a Security Council resolution authorizing intervention, each ally assumed the responsibility for choosing its own juridical basis for approving NATO military action decisions, a precedent that may prove appropriate in some future circumstances.)