The killing of Maj. Gen. Qassim Suleimani, Iran’s most formidable military and intelligence leader, displayed the fault lines in a fractious region. From Iraq to Israel, many victims of the commander’s shadow warfare celebrated his death; but in Tehran, thousands filled the streets to grieve. Today, we explore who General Suleimani was, and what he meant to Iranians. Guest: Farnaz Fassihi, a reporter covering Iran for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily. Background reading:As we break down how religious differences have fueled conflict in Iraq and Iran, here’s a refresher on the distinction between Sunni and Shia Islam. At General Suleimani’s funeral, a senior military leader vowed to set America “ablaze.” But it remains uncertain how, or even whether, Iran will strike back.President Trump and his defense secretary have said different things about how the United States might respond to any Iranian retaliation. One of our Interpreter columnists is struggling to see a deeper strategy.Dozens of American citizens of Iranian descent have been detained while trying to enter the United States. “My kids shouldn’t experience such things,” one woman said after being held overnight upon return from a ski trip in Canada. “They are U.S. citizens. This is not O.K.”