An Iran-backed militia seeking to rule a divided country devastated by civil war has managed to redraw the world trade map with a low-cost strategy of attacking shipping’s soft targets.

The campaign by the Houthi leadership has so far sunk two ships, killed four seafarers, forced hundreds of ships to take more treacherous routes around the Cape of Good Hope and wiped billions of dollars from Egypt’s economy as the toll-taker at the gateway to the Red Sea.