To wage war in Yemen, Saudi Arabia is using F-15 fighter jets bought fromBoeing. Pilots from the United Arab Emirates are flying Lockheed Martin’s F-16 to bomb both Yemen and Syria. Soon, the Emirates are expected to complete a deal with General Atomics for a fleet of Predator drones to run spying missions in their neighborhood.

As the Middle East descends into proxy wars, sectarian conflicts and battles against terrorist networks, countries in the region that have stockpiled American military hardware are now actually using it and wanting more. The result is a boom for American defense contractors looking for foreign business in an era of shrinking Pentagon budgets — but also the prospect of a dangerous new arms race in a region where the map of alliances has been sharply redrawn.

Last week, defense industry officials told Congress that they were expecting within days a request from Arab allies fighting the Islamic State — Saudi Arabia, the Emirates, Qatar, Bahrain, Jordan and Egypt — to buy thousands of American-made missiles, bombs and other weapons, replenishing an arsenal that has been depleted over the past year. […]