Dar es Salaam, TanzaniaOne evening in March, as a warm breeze blew in from the Indian Ocean and the call to prayer from the neighborhood mosque echoed in the twilight, Omari Abdullah sat on a plastic chair outside his home, preparing for his night’s work.

Like many in this sprawling seaside metropolis, Abdullah is a migrant—a country boy drawn to life in the big city, who arrived 17 years ago and never looked back. A native of Kigoma, in western Tanzania, he couldn’t afford high school and grew restless with his job on a sunflower farm. So at 20 he made the 800-mile journey on the back of a truck, stayed with a friend until he could find work, and eventually started his own