May 17th 2013, 14:03 by Economist.com

A guide to the key rebel forces in Syria

AS THE civil war in Syria has dragged on, the rebels have become more Islamist and extreme. For Western governments pondering whether to arm them, Jabhat al-Nusra (Victory Front) is the biggest worry. Its global jihadist ideology justifies violence to bring about a nation where all Muslims unite. It enjoys murky sources of private funding, including regular payments from al-Qaeda in Iraq. Ahrar al-Sham has more local aims, but its comrades are also vehemently Islamist. Other umbrella groups, such as Liwa al-Tawhid in Aleppo, Syria’s embattled second city, are harder to classify, in part because they serve as franchises or bring together smaller groups with a range of ideas. The Farouq Battalions, whose territorial reach goes from Homs to Hasaka in the north-east, is another mixed bag, ranging from Islamists to people with no particular ideology. The Supreme Military Command, led by General Salim Idriss, a Sunni defector from President Assad’s army, includes some able commanders but still lacks the cash and arms to match either the regime’s forces or Jabhat al-Nusra, which ignores the military command. Ominously, rebels from more secular-minded or more moderately Islamist groups speak openly of a second war to come—against Jabhat al-Nusra. See full article.