A Specialised Criminal Court in Saudi Arabia has sentenced a prominent Shia clergyman, Sheikh Nimr Baqir al-Nimr, to death on vague charges of “breaking allegiance to the ruler” and “encouraging, leading and participating in demonstrations.”

It is a sentence that is creating rage among Saudi Arabia’s two-million-strong Shia minority that has long claimed to be persecuted and discriminated against.

The Saudi authorities are nervous about how the verdict handed down on 15 October will be received; the court arrested Sheikh Nimr’s brother, Mohammed Nimr al-Nimr, after he announced the outcome of the trial on Twitter. Local activists believe this was to prevent him speaking to the media after sentencing. Harsh though the sentence is, it is less than the prosecution’s demand for execution by “crucifixion”, a punishment that in Saudi Arabia involves beheading.

Sheikh Nimr had been under arrest since 2012 when he was shot four times in the leg by police, who claimed that he resisted them with a weapon when they were trying to arrest him. His family dispute this, saying that he did not own a weapon and accusing the Saudi authorities of not providing adequate medical treatment for his wounds. Sheikh Nimr had earlier said in an interview with the BBC that he looked to “the roar of the word against the Saudi authorities rather than weapons … the weapon of the word is stronger than bullets, because authorities will profit from a battle of weapons”. At the time of his arrest there were riots in Eastern Province, the site of much of Saudi Arabia’s oil wealth, in which three people were killed.

News of Sheikh Nimr’s death sentence received limited coverage in the foreign media which was focused more on the outcome of the Islamic State’s siege of Kobani in northern Syria. It was a more obviously significant development and was, moreover, taking place in full view of television cameras just across the border in Turkey. But these two events in Saudi Arabia and Syria are linked because they are both part of the greatest crisis in the Middle East since the fall of the Ottoman Empire a century ago.

Sheikh Nimr’s sentence is important because of its negative impact on the Shia in Saudi Arabia and their fraught relationship with the Saudi royal family. But it has a wider significance because it helps deepen hostility between Shia and Sunni Muslims and escalates the struggle between them everywhere in the world. Syria and Iraq are the main arena for this battle, but it now encompasses all 1.6 billion Muslims, a quarter of the world’s population.

It is a persistent error by the United States, Britain and their allies in the West to underestimate the extent to which the Sunni-Shia confrontation determines what happens in the Middle East. This is particularly so in those countries in which the Shia, or sects demonised by Sunni governments as Shia, form a significant part of the population. The blindness of the western powers is to a degree self-serving and intentional: it makes it easier for them to ally themselves with the theocratic absolute monarchies of the Gulf without having to admit they have thereby plugged into a bigoted and sectarian agenda.

The Sunni-Shia battle is growing by the day involving communities like the Alawites of Syria, the Alevi of Turkey and the Houthi of Yemen, whose Shia credentials might have been doubted a few decades ago by the Shia of Iran, Iraq and Lebanon. But people’s national and religious identities are defined as much by the perceptions and actions of their enemies as by their own beliefs. Denunciations of the Houthi of Yemen, who have recently captured the capital Sanaa, by Saudis as Shia and pawns of Iran tend to be self-fulfilling. When I asked some Alevi in Istanbul last year if they saw themselves as part of the wider Shia world, they said that their problem was that many Sunni saw them as such.

The same is true of Syria. Whatever the popular origins of the revolt against President Bashar al-Assad and his government in 2011, it swiftly took a sectarian form. This happened because sectarian divisions were always very real and because Sunni states like Saudi Arabia and Turkey channelled their support towards jihadis, thus preparing the ground for the dominance of the rebel movement by Islamic State (IS) and Jabhat al-Nusra, al-Qa’ida’s affiliate in Syria.

It has been politically convenient for the US, Britain and their allies to pretend that there is a “moderate” non-jihadi rebel movement capable of fighting both IS and the Assad government. In reality, the civil war in Syria is all too real and sectarian killers are not all confined to IS. Earlier this year I was on the outskirts of Adra, a town north of Damascus, part of which had been captured by rebels from Douma who had killed many non-Sunni. One highly secular Alawite family had blown themselves up with grenades, children as well as parents, because they believed they would all be tortured to death by the rebels.

In Syria the western powers blithely pretend that the rebels, especially the famous “moderates” are less sectarian than they are. In Baghdad they do the exact opposite and pretend that the Shia-dominated government and its armed forces do not have a sectarian agenda. The reality is that the most effective military force on the government side is the Shia militias who murder and kidnap Sunni with impunity as shown by a recent Amnesty International report. If the United States and others back the government with embedded advisers calling in air strikes, it will be supporting the Shia in a war against the 5 or 6 million Sunni in Iraq. Anti-Sunni sectarian cleansing has already started in Diyala, Hilla and other provinces around Baghdad. It is self-deceiving to believe the recapture of Mosul or other Sunni cities by the government will be welcomed by the terrified local inhabitants.

ORDER IT NOW

These sectarian wars cannot really be won by either side. The most positive thing that outside powers can do in Syria is to arrange a ceasefire between anti-IS forces, both government and rebel. Hatred is too great for a political solution in Syria, but a truce is feasible if backed by outside powers such as the US, Russia, Iran, Saudi Arabia and Turkey.

When it comes to the broader Sunni-Shia confrontation, the US, Britain and their allies need to end their blindness, calculated though it is, towards the Sunni sectarianism of Saudi Arabia and the Gulf monarchies. Speaking of Sheikh Nimr, Yusuf al-Khoei, a prominent campaigner for Shia-Sunni dialogue, says “it makes a mockery of Saudi claims to be fighting extremism when they threaten to kill a prominent member of the Shia community in their country. It makes it impossible to have a dialogue with them.”

In many respects the situation in Saudi Arabia is getting worse rather than better with a surge in the number of executions, as if the government feels it must compete with the IS by demonstrating the rigour with which it implements Islamic law (Sharia) and deals with Shia, Christians and others who do not follow its own brand of Islam.