The Boston Globe has made Jean Bethke Elshtain’s essay on just war theory (published last fall) available on-line. The crucial issue she highlights is the one that has divided liberals who regard national sovereignty as sacrosanct from those who see compelling reasons to sometimes disregard national sovereignty:
In my view, however, just war demands that we see a sovereign state as an actor that either does what states are supposed to do — provide basic civic peace, rule of law, and security for citizens — or does not. When a state destroys or is prepared to destroy its own citizens and to propel its violence outside its own borders, it becomes a criminal entity. Under just war theory, states themselves must often come under severe moral scrutiny.
She goes on to argue that Iraq has failed to be a legitimate state, although one piece of evidence she cites — a link between Saddam Hussein and al Qaeda — seems highly unlikely to me. Still, this is the basic issue that tipped me toward the interventionist camp.