The main criticism of US policy in Syria has long been that President Barack Obama should have used US military force or more aggressive arms aid to strengthen the armed opposition to Assad. The easy answer is that the whole idea that there was a viable non-extremist force to be strengthened is a myth – albeit one that certain political figures in London and Washington refuse to give up.

But the question that should have been debated is why the Obama administration acquiesced to its allies funding and supplying a group of unsavoury sectarian armed groups to overthrow the Assad regime.

That US acquiescence is largely responsible for a horrible bloodletting that has now killed as many as 400,000 Syrians. Worse yet, there is still no way to end the war without the serious threat of sectarian retribution against the losers.

"The Obama administration bears responsibility for this atrocity, because it could have prevented Turkey, Qatar and Saudi Arabia from launching their foolishly adventurous war in Syria. None of them did so out of desperate need; it was a war of choice in every case. And each of the three states is part of the US security system in the Middle East, providing military bases to NATO or to the United States and depending on US support for its security.

But instead of insisting that those three Sunni allies reconsider their options, the Obama administration gave the green light at a conference in Riyadh at the end of March 2012 for proceeding with arming those who wanted to replace the regime, leaving the United States ostensibly free to be a peacemaker. As Hillary Clinton put it at the Riyadh conference: "Some will be able to do certain things, and others will do other things."

The policymakers responsible for Syria should have known that the seeds of violent sectarian conflict had already been planted in Syria by the early 1980s and that the present war was deeply infected by sectarianism from the beginning. They knew that the Assad regime ruled from the beginning with an iron hand primarily to protect the interests of the Alawites, but also to protect the Christian and Druze minorities against Sunni sectarianism. 

The faction of the banned Muslim Brotherhood based in Hama adopted a decidedly sectarian line toward the Alawites, not only referring to the Ba'athist government as an "apostate regime" and sought its violent overthrow, but also demonstrated a readiness to kill Alawites, simply because they were not regarded as true believers in Islam.

After the initial failed armed struggle against the regime, the organisers were forced into exile, but in 1979 an underground member of the Fighting Vanguard faction of the Brotherhood named Ibrahim al-Yousef, who had infiltrated the Syrian army artillery school in Aleppo, separated all the Alawite cadets from the non-Alawites and then shot 32 of them dead and wounded 54 before escaping.

In 1980, after the Brotherhood made an unsuccessful attempt to assassinate Hafez al-Assad himself, the regime took swift and brutal retribution: the very next morning, between 600 and 1,000 Brotherhood prisoners were killed in their cells.  

Sectarian violence in Syria reached its climax in 1982, when the Syrian army went into Hama to break the Brotherhood's control over the city. The operation began when Syrian army troops entered the city to get individuals on its list of Brotherhood members, but were mowed down by Brotherhood machine gunners. Thousands more regime troops were sent to the city, and the Brotherhood mobilised the entire Sunni population to fight. The mosques blared the message, "Rise up and drive the unbelievers from Hama," as Thomas L. Friedman recounted in 1989.