The annual Hajj, the pilgrimage to the holy city of Mecca every Muslim is obligated to make at least once in his or her lifetime, began on Wednesday with more than 2 million worshippers from around the world in attendance. A rapprochement between Saudi Arabia and Iran has allowed pilgrims from the Islamic Republic to return for the first time since more than 2,000 were killed when a stampede broke out in 2015. That, in addition to a dispute over the execution by the Saudis of a Shiite cleric, resulted in relations between the two powers being broken. This year the break-down in relations between the Saudis and several other Arab nations and Qatar has marred the feeling of unity although Riyadh lifted the formal ban on Qatari participation shortly before the pilgrimage began. The threat of terror from the Islamic State also weighs on the minds of Hajj organizers. On Thursday, hundreds of thousands will climb Mt. Arafat in Mina after first performing the ritual walk (tawaf) around the black cube (Kaaba) in the center of Mecca’s Grand Mosque. It is the Kaaba toward which Muslims around the world face when praying.