The myth of an endless conflict between Sunnis and Shiites across the Middle East ever since the Battle of Karbala has been ablydebunked by various writers, who point to far more modern roots—perhaps 1979 and the Iranian Revolution— for the divide. In Saudi Arabia, however, the battle between Shiites and Sunnis runs back at least a century. The country’s Shia population is concentrated in al-Ahsa, an eastern province. The area abuts Bahrain, where Shiites make up a majority of the population but the ruling family is Sunni.

Tension between Sunnis and Shiites in Saudi Arabia (and elsewhere) increased following the Iranian Revolution in 1979, which replaced the shah’s government with a theocratic regime, the Council on Foreign Relations says:

The transformation of Iran into an overtly Shia power after the Islamic revolution induced Saudi Arabia to accelerate the propagation of Wahhabism, as both countries revived a centuries-old sectarian rivalry over the true interpretation of Islam. Many of the groups responsible for sectarian violence that has occurred in the region and across the Muslim world since 1979 can be traced to Saudi and Iranian sources.

One estimate found that since 1979, the Saudi government had jailed, exiled, or executed hundreds of Shiites. “Saudi recruits for al-Qaeda and the Islamic State group are often motivated by a desire to contain Shiism and stem Iranian influence in the region—strategic objectives that Saudi media perpetuates ad infinitum,” writes Toby Mathiessen. “Anti-Shiite (and anti-Christian and anti-Jewish) incitement is spread across the region by Saudi-based television channels.”

At the same time the revolution, in 1979, Nimr was leaving Saudi Arabia to study in Iran, as many Shia clerics do. He returned in 1994, where The Guardian reports he became well known to state security but remained otherwise obscure: “The kingdom’s intelligence services questioned him frequently, largely over his calls for increased religious freedom. He was eventually detained in 2003 for leading public prayers in his home village, where he had become an imam.”

Nimr was overshadowed by more prominent Shiites—on one side, Hassan al-Saffar, who favored dialogue and reconciliation with the Saudi monarchy, and on the other by groups like Saudi Hezbollah that unapologetically backed violence against the state. Nimr told the State Department that the interfaith efforts were a “sham” and argued that only instability and tumult—rather than gradual change—would better the position of Saudi Shiites. But he hedged on whether he backed violence:

When asked by [a State Department political officer] as to whether his tough talk promoted violence or simply warned of it as a possible repercussion of continued discontent in the Shi’a community, al-Nimr responded that if a conflict were to occur he would « side with the people, never with the government. » He continued by saying that though he will always choose the side of the people, this does not necessarily mean that he will always support all of the people’s actions, for example, violence.

The State Department cable added Nimr was gaining popularity among young people. His stature grew in spring 2009, after Shia pilgrims clashed with security forces in Medina over access to holy sites; Nimr denounced the security forces, but then was forced to go into hiding to avoid arrest. By January 2010, the State Department reported in another cable that Nimr had returned home and was living under something like house arrest. The diplomat, who wrote that cable, judged that Nimr had overestimated his sway, gone too big, and as a result had lost his influence. A neighbor said that the government “chose not to pursue him further out of concern they would elevate his status.”

“In any place he rules—Bahrain, here, in Yemen, in Egypt, or in any place—the unjust ruler is hated,” Nimr said. “Whoever defends the oppressor is his partner with him in oppression, and whoever is with the oppressed shares with him his reward from God.” He also denounced the king and his family as “tyrants,” saying: “We don’t accept al-Saud as rulers. We don’t accept them and want to remove them.”

In another 2011 speech, Nimr said, “From the day I was born and to this day, I’ve never felt safe or secure in this country. We are not loyal to other countries or authorities, nor are we loyal to this country. What is this country? The regime that oppresses me? The regime that steals my money, sheds my blood, and violates my honor?”

That was all too much for the regime, and in 2012 it moved to arrest him. But during his apprehension, police claimed they came under fire. Nimr was shot in the leg. He was charged with sedition and various terrorism-related crimes. In his absence and persecution, Nirm’s popularity soared. There were “near-nightly protests [at his mosque] and elsewhere in the Eastern Province,” wrote Frederic Wehrey of the Carnegie Endowment for International Peace in 2013. “Nimr speaks to what we are feeling in hearts,” a young activist told Wehrey. A cleric added, “Awamiya is just the opening of the volcano, and you don’t judge the size of the volcano from its opening.” Wehrey reported little change in the area since the height of the 2011 demonstrations. Many Shiites put more faith in interfaith dialogue than did Nimr, but they were frustrated by reticence among hardline Sunnis.

Protests once again died down. Then, on October 15, 2014, Nimr was sentenced to death, and unrest broke out again. The timing of the sentence baffled some observers, who said it was simply stoking resentment all over again. Matthiessen suggested it might be an attempt to assuage criticism over the Saudi government’s sentencing of Sunni alleged terrorists to death—evidence for naysayers that Sunnis and Shiites alike would be dealt with harshly. The sentence also drew condemnation from Iran.

(Since then, Saudi Arabia and Iran have been in frequent tension on a variety of matters: the Iranian nuclear deal, a diplomatic effort to bring peace to Syria, and the deadly stampede at the Hajj in September.)

Nimr’s execution, along with 46 others, on Sunday once again jumpstarted protests that had gone dormant. This time, however, the backlash wasn’t just in al-Ahsa—it was in Bahrain, and in Lebanon, and from Yemen’s Houthi rebels, a Shia insurgency that has been targeted by months of Saudi bombings. And it was in Iran, where demonstrators marched in the streets and sacked and burned the Saudi embassy, triggering a break in diplomatic relations. The immediate effect of the execution and protests has been to make the Middle East into an even less stable place than it seemed before. Once again, the broader geopolitical turbulence has overshadowed Saudi Arabia’s Shiites.