Worldwide, violence is on the decline, but in the crowded cities of the global south — cities like Aleppo, Bamako and Caracas — violence is actually accelerating, fueled by the drug trade, mass unemployment and civil unrest. Security researcher Robert Muggah turns our attention toward these "fragile cities," super-fast-growing places where infrastructure is weak and government often ineffective. He shows us the four big risks we face, and offers a way to change course.