With Saudi Arabia participating in air strikes, the kingdom is now fully engaged in a broad-based coalition that is prepared to take the fight to the Islamic State in Iraq and Syria (Isis). But the kingdom’s discomfort at the situation it finds itself in is evident; lining up alongside the Shia-dominated regime in Baghdad, and serving goals that ultimately play into the hands of both Damascus and Tehran, this is emphatically not a conflict of Riyadh’s choosing.

Nonetheless, the House of Saud has plenty of reasons to want to see the containment – and eventual defeat – of Isis. The jihadist group’s claim to a sizeable caliphate stretching from Aleppo to Mosul represents a direct challenge to the primacy of Saudi Arabia’s claim to a special position at the helm of the Muslim world. Isis has taken care to deploy language echoing that of the kingdom’s Wahhabi creed, in a transparent effort to undercut Saudi religious legitimacy. It has sent stark warnings that the kingdom’s participation in the US-led military campaign will have dire consequences.

The ramifications of Isis embedding itself further across Syria and Iraq, and threatening Riyadh’s allies Lebanon and Jordan, do not bear thinking about. While the Saudis have learned to live with the revolutionary clerical regime in Iran for the past 35 years, that is in large part due to it being a Shia country. A Sunni caliphate, drawing support from across the region – including the kingdom itself — is a very different kettle of fish. The danger of blowback suggests there is no room to brook its continued existence. At the risk of propping up hated regimes in Syria and Iran, Saudi Arabia has reluctantly concluded it must put its resources at the disposal of the US air campaign.