Geography is destiny:
Port-au-Prince was never an easy place to live. Sixty million years ago, the land under it was caught in the middle when the buoyant continental crust of North America crashed into the Caribbean Plate. The two plates had been pushing against each other for ages, forcing up from the seabed an arc of islands that would one day be known as the Greater Antilles. Then came a jolt so violent that it the plates’ direction, catching the arc in a sideswiping collision that would slowly tear each island to splinters. On the second-largest island of the Greater Antilles, these shearing forces forged the highest mountains and deepest troughs of the archipelago. On its northern half rose the Massif du Nord; in the southwest, the Massif de la Hotte and Massif de la Salle. Between these mountains , at the foot of where the Caribbean was being pushed over the volcanic terrane, was a solitary lowland depression just seven and a half miles wide. That is where Port-au-Prince would be built.
---from The Big Truck That Went By: How the World Came to Save Haiti and Left Behind a Disaster by Jonathan M. Katz.