The civil war in Syria, one of the few lasting legacies of the Arab Spring, has been under way for more than two years. There has been substantial outside intervention in the war. The Iranians in particular, and the Russians to a lesser extent, have supported the Alawites under Bashar al Assad. The Saudis and some of the Gulf States have supported the Sunni insurgents in various ways. The Americans, Europeans and Israelis, however, have for the most part avoided involvement.

Last week the possibility of intervention increased. The Americans and Europeans have had no appetite for intervention after their experiences in Afghanistan, Iraq and Libya. At the same time, they have not wanted to be in a position where intervention was simply ruled out. Therefore, they identified a redline that, if crossed, would force them to reconsider intervention: the use of chemical weapons.

There were two reasons for this particular boundary. The first was that the United States and European states have a systemic aversion to the possession and usage of weapons of mass destruction in other countries. They see this ultimately as a threat to them, particularly if such weapons are in the hands of non-state users. But there was a more particular reason in Syria. No one thought that al Assad was reckless enough to use chemical weapons because they felt that his entire strategy depended on avoiding U.S. and European intervention, and that therefore he would never cross the redline. This was comforting to the Americans and Europeans because it allowed them to appear decisive while avoiding the risk of having to do anything.

However, in recent weeks, first the United Kingdom and France and then Israel and the United States asserted that the al Assad regime had used chemical weapons. No one could point to an incidence of massive deaths in Syria, and the evidence of usage was vague enough that no one was required to act immediately.

In Iraq, it turned out there was not a nuclear program or the clandestine chemical and biological weapons programs that intelligence had indicated. Had there been, the U.S. invasion might have had more international support, but it is doubtful it would have had a better outcome. The United States would have still forced the Sunnis into a desperate position, the Iranians would have still supported Shiite militias and the Kurds would have still tried to use the chaos to build an autonomous Kurdish region. The conflict would have still been fought and its final outcome would not have looked very different from how it does now.

What the United States learned in Iraq, Afghanistan and Libya is that it is relatively easy for a conventional force to destroy a government. It is much harder -- if not impossible -- to use the same force to impose a new type of government. The government that follows might be in some moral sense better than what preceded it -- it is difficult to imagine a more vile regime than Saddam Hussein's -- but the regime that replaces it will first be called chaos, followed by another regime that survives to the extent that it holds the United States at arm's length. Therefore, redline or not, few want to get involved in another intervention pivoting on weapons of mass destruction.

Interventionist Arguments and Illusions

However, there are those who want to intervene for moral reasons. In Syria, there is the same moral issue that there was in Iraq. The existing regime is corrupt and vicious. It should not be forgotten that the al Assad regime conducted a massacre in the city of Hama in 1982 in which tens of thousands of Sunnis were killed for opposing the regime. The regime carried out constant violations of human rights and endless brutality. There was nothing new in this, and the world was able to act fairly indifferent to the events, since it was still possible to create media blackouts in those days. Syria's patron, the Soviet Union, protected it, and challenging the Syrian regime would be a challenge to the Soviet Union. It was a fight that few wanted to wage because the risks were seen as too high.

The situation is different today. Syria's major patron is Iran, which had (until its reversal in Syria) been moving toward a reshaping of the balance of power in the region. Thus, from the point of view of the American right, an intervention is morally required to confront evil regimes. There are those on the left who also want intervention. In the 1980s, the primary concern of the left was the threat of nuclear war, and they saw any intervention as destabilizing a precarious balance. That concern is gone, and advocacy for military intervention to protect human rights is a significant if not universal theme on the left.