In two weeks, it will be the one-year anniversary of a major action in the Red Sea: the Houthis, a powerful group from Yemen, began blocking ships they suspect are linked to Israel and Western countries. This blockade has caused big disruptions to international shipping, especially in waters around Yemen, and it shows no sign of slowing down. The Houthis have even started raising funds to support their campaign against Israel and its allies.

Here’s how they’re doing it: The Houthis are a...