BAGHDAD — Militia justice is simple, the fighters explained. “We break into an area and kill the ones who are threatening people,” said one 18-year-old fighter with Asaib Ahl al-Haq, a Shiite militia that operates as a vigilante force around Baghdad. Another 18-year-old fighter agreed. “We receive orders and carry out attacks immediately,” he said, insisting that their militia commanders had been given authority by Iraqi security officials. That free hand has helped make Asaib Ahl al-Haq the largest and most formidable of the Iranian-backed Shiite militias that now dominate Baghdad. Once a leading killer of American troops, the militia is spearheading the fight against the Sunni extremists of the Islamic State, also known by the acronyms ISIS and ISIL. That means Asaib Ahl al-Haq and the United States military are now fighting on the same side, though each insists they will not work together. But the power and […]