On a congested road out of Mokha, a motorcycle overturned. Alaa Ali Salem, fleeing Yemen's newly fallen port city with his wife and children, picked himself up from the tarmac — injured, disoriented, and unsure where to go. His account is one of tens of thousands now accumulating across the country's south, as Iran-backed Houthi rebels complete a swift territorial advance that is alarming not only Yemenis, but shipping executives and strategists from London to Beijing. The International Organization for Migration reported on Saturday that at least 76,000 people had been displaced since July — a figure that had stood at 46,000 just days earlier.

The speed of that rise reflects the pace of the Houthi push: fighters seized the Red Sea port of Mokha on Thursday and, by Friday, had taken Mayun Island — also known as Perim — which sits directly astride the Bab el-Mandeb Strait. That narrow chokepoint, where the Red Sea meets the Gulf of Aden, carries a significant share of global crude oil and container traffic. Roughly 1,400 civilians crossed the water to Djibouti within a single 24-hour period, according to that country's minister of economy, Ilyas Moussa Dawaleh. The strategic consequences extend well beyond Yemen's borders.

The Bab el-Mandeb had already assumed greater importance after Houthi attacks on Saudi tankers effectively closed off an alternative route through the Strait of Hormuz for Gulf oil exports headed to Asian markets. With Houthi forces now controlling Mokha, Mayun, the capital Sanaa, and the western port of Hodeida, their leverage over regional trade has grown considerably. Although Houthi officials have sought to reassure shipowners that only Saudi-linked vessels face interdiction, the credibility of such assurances is, at best, uncertain. For civilians like Durrah Ali Hassan, who found shelter in a relative's house in Aden after watching soldiers shout orders to retreat as gunfire erupted around her, the geopolitical calculus is a distant abstraction.