Having rejected the diplomatic option of talking to Assad, neither the US nor Britain can lead from behind
It was only a matter of time before a proxy war between regional powers turned into a battlefield in which foreign fighters openly engaged in combat. Hezbollah's fighters had been present in Syria for some time, but their overt role in the fight for a strategic border town linking Damascus to Homs and the regime's core support in the Alawite hinterland is, potentially, a game-changer. If it ever had been an open question whether conditions could be produced that would allow Iran and Hezbollah to relinquish their support for Bashar Assad, in favour of a transitional regime that would offer guarantees to the minority Alawite community, that has now been answered.
Whatever happens in the town of Qusair, both Hezbollah and Iran are now signalling that Assad's fate has become a matter of existential survival for them, too. The regime's victory, or defeat, will become a victory or defeat for its allies. This makes any attempt at intra-Syrian reconciliation – already a faint hope, after the vicious sectarianism shown first by the regime and latterly, alas, by some rebels – virtually impossible. Syria of any description, either the north and east, still held by the rebels, or the south and west, held by the regime, is no longer master of its own territory or fate.
Factionalism is rife. The dominant, or at least most cohesive, fighting group on the rebel side, Jabhat al-Nusra, is funded and armed by non-state actors, as is al-Qaida, to which the Sunni jihadi group has vowed its allegiance. There are splits between rebel units on the ground and the Syrian opposition in Turkey and Doha. A further cleavage has opened between Saudi Arabia, United Arab Emirates and Jordan, on the one side – all determined not to let the Islamists of the Muslim Brotherhood gain control of Syria – and Qatar and Turkey on the other, which back other brotherhood-dominated regimes in Egypt and Tunisia. If Sunni al-Qaida is fighting Shia Hezbollah in Qusair, the Sunni regimes of the Gulf are doing a good job undermining each other's foreign policy as well.
Did the Israeli strikes provoke Hezbollah's move? As Vladimir Putin told Binyamin Netanyahu in no uncertain terms, they certainly prompted Russia into sending Assad S300 surface-to-air missiles. The involvement of the best armed and trained Shia militia in the region was perhaps only a matter of time. The foreign secretary, William Hague, said there was a compelling case for lifting the EU arms embargo, dispatching weapons in "carefully controlled circumstances". This is provocative. We have lost leverage over rebel groups. Having rejected the diplomatic option of talking to Assad for so long, neither US nor Britain — nor Russia on its side — can "lead from behind" in Syria. A military conflict is no place for back-seat drivers.