“Two years from now, this place is going to be empty,” General Amos told the company. “What you’re doing here will have paid off.”

But as the Marines shift from Helmand to assignments in the Middle East, Africa and the Pacific, a question looms: Was it all worth it?

General Amos says he has little doubt that it was. The number of violent events, from gunshots to roadside bombs, has dropped in almost every district since 2010, Marine commanders say, though the figures are still being finalized. Roads have been paved and markets secured, allowing commerce to grow in places like Marja, Nad Ali and Lashkar Gah, the provincial capital. Civilian casualties are down by 20 percent.

As Marine and British forces have drawn down, the Afghan National Army has grown, to almost four brigades with more than 16,000 soldiers. Those forces now patrol much of southern Helmand independently, the Marines say. In a few months, they will be responsible for securing the rest of the province with much less, and more distant, NATO support.