Similar efforts preceded ISIS’s seizure of Mosul and parts of Anbar province across the border in Iraq; the months before the ISIS surge were marked by assassinations. “They have agents and spies everywhere,” an Iraqi military officer, an Anbar native, told me from hiding in the summer of 2014, explaining that ISIS knew the names, ranks, home addresses, and salaries of police officers and soldiers throughout the areas it had recently seized.

From there, ISIS used a reign of terror to keep millions of Syrians and Iraqis in its clutches. It claimed them as citizens of its hard-line state, but in reality they were hostages. The way most Syrians and Iraqis experienced the group was as a brutally effective intelligence agency. Neighbors informed on one another; dissent was punished. Even in southern Turkey, where I met the rebel commander in question, Syrians were afraid to discuss the group, wary of retribution. Conversations about ISIS in the region’s hotels and cafés were hushed and nervous, as people worried about—even in Turkey, a NATO member state—who might be listening. Just as in Syria and Iraq, ISIS had established underground cells throughout the country.

The shadowy, lurking aspect of Baghdadi also defined his image internationally. He gave just a single public speech: a sermon in Mosul’s Great Mosque of al-Nuri in July 2014, during which he claimed the restoration of the caliphate, an idea that was an abomination to all but a tiny fraction of the world’s 1.8 billion Muslims. Citizens of Europe, the United States, and other places that were subject to Baghdadi’s terrorist ambitions experienced him less as the self-styled Caliph Ibrahim than as a purveyor of murky, senseless violence.

Where Osama bin Laden focused his efforts on spectacular attacks, Baghdadi stood out for promoting the idea that any sort of violence would do. ISIS carried out horrific mass-casualty attacks: killing more than 100 in Ankara in October 2015 and in Paris the following month, as well as dozens more in Brussels in March 2016, in Istanbul in January 2017, and in Manchester in May 2017. It also carried out an endless series of lower-grade atrocities: stabbing passersby, driving vehicles into crowds. And it encouraged lone wolves, such as the Orlando, Florida, nightclub shooter, to carry out attacks in its name.

The sum of all this was to promote the idea that anyone could be a threat. It was designed to make people suspicious of their neighbors, or of newly arrived refugees. It pitted people against one another.

This is worth remembering as Donald Trump takes credit for Baghdadi’s death, because Trump himself helped advance this part of Baghdadi’s cause. As the journalist Murtaza Hussain argued in the wake of the Paris attacks, ISIS was seeking to eliminate what it called the “gray zone” of co-existence between Muslims and the West. “By launching increasingly shocking attacks against Western targets, the Islamic State is pursuing a specific goal—generating hostility between domestic Muslim populations and the broader societies that they live in,” Hussain wrote. “[It] is consciously seeking to trigger a backlash by Western governments and citizens against the Muslim minorities living in their societies. By achieving this, the group hopes to polarize both sides against each other, locking them into an escalating spiral of alienation, hatred and collective retribution.”