Should Israel Intervene in the Syrian Civil War?

Bashar al-Assad's forces have lost control of Syria's border with Israel, which is now held jointly by the al-Qaeda-linked Nusra Front and non-Islamist Sunni rebels. Israel has been quietly providing assistance to the latter. But with the growing threat of Nusra Front dominance, and the possibility of an Islamic State takeover, a more active approach is called for, contends Ehud Yaari: