President Obama will seek authority from Congress to use military force against Syria because Syrian President Assad allegedly used chemical weapons on his own people. The evidence of chemical weapons use seems overwhelming.,
History should remind us, however, that George W. Bush convinced many that Saddam Hussein had massive stockpiles of WMDs. None were found. George H. W. Bush was aided in his efforts to go to war in Kuwait when stories surfaced about Iraqi soldiers removing babies from hospital incubators and leaving them to die. Those stories were fabrications.
Skepticism aside, there are major principles to follow before going to war. The most simple elements of just war theory include just cause, comparative justice, competent authority, right intention, probability of success, last resort, proportionality.
Upholding international norms against using chemical weapons against civilians meets the criteria for a just cause. Further, Assad's use of chemical weapons disproportionately affected the civilians even if they actively supported the forces opposed to Assad. The comparative justice criterion seemingly has been met.
President Obama is requesting Congress to approve limited strikes to punish Assad for chemical weapons use. If Congress grants approval, war will have authorized by proper authority and force will be used with right intention. Assad is a stubborn man, so this may well be a last resort. Limited strikes seems proportional as well.
The probability of success, however, does not exist. The military strike will not topple the Assad regime. A military strike will not take out chemical weapon stockpiles because such a strike will disperse the chemical agents. Assad will, therefore, remain in power and be able to use chemical weapons again. More importantly, the forces against Assad contain elements as dangerous as he is, so it's unclear that it's in anyone's best interest to have those on the other side come to power.
This situation does not involve self-defense; it will do little to hamper or deter Assad. More importantly, weakening Assad may be a Pyrrhic victory. In that light, military force in Syria is not justified.