From his modest office in the shrine city of Najaf, Iraq’s highest religious authority, Grand Ayatollah Ali al-Sistani, leader of the country’s Shiite establishment, issued a call to arms asking his followers to join with the government military to stop the blitzkrieg by the Islamic State in Iraq and Syria. But one cleric, Moktada al-Sadr, who led a militia that fought the government and lost in 2008, decided instead that he too would challenge the state. Mr. Sadr revived his Mahdi Army, possibly one of the largest and most experienced battle groups in Iraq, and announced that under no circumstances would it be under the control of the government. His open challenge to Iraq’s Shiite establishment lays bare the latest in a series of cracks that are dividing the country’s three main ethnic groups, the Shiites, Sunnis and Kurds, as the Iraqi state comes unraveled. But […]