Last summer, with Iraq's army weakened, and the Islamic State advancing on Baghdad, the country's Iran-backed Shia militias were called on halt the militants’ progress. While successful in combat, their growing influence has led many to fear that the militias threaten the country's sectarian and political balance. Henry Langston traveled to Iraq for VICE News to witness firsthand how Shia militias are taking the fight to the Islamic State, and to document the fallout of their rise to power.