WASHINGTON - In measuring progress in the American-led air war against the Islamic State in Syria and Iraq, bombing numbers tell one story but results tell another.

Fighter jets, bombers, attack planes and drones are dropping an average of 2,228 bombs per month on targets ranging from militant snipers and machine gun positions to oil facilities, weapon storage shacks, bulldozers and buildings. The attacks have killed upward of 20,000 Islamic State fighters.

But the bottom-line result has been stalemate. The reasons are twofold: The U.S. is deliberately taking a gradualist approach by air, and it has chosen to wait for local ground forces to emerge to retake territory rather than sending in large numbers of its own combat troops. This has given the militants time and space to consolidate their gains.