The 24th Marine Expeditionary Unit moved into the town of Garmser in late April. It's the farthest south that U.S. forces have been in Afghanistan in years.

Marine commanders say the Taliban brought in arms and fighters in response, to protect the lucrative poppy fields that cover Garmser. The Taliban derives tens of millions of dollars from the poppy trade each year by taxing farmers and charging safe-passage fees.

The Marines originally planned to be in Garmser for only a couple of days, to open a road that leads to southern Helmand, near the border with Pakistan. But the 24th MEU decided to extend its stay to root out the fighters.

After weeks of skirmishes with insurgents - who fired rockets and mortars at U.S. positions several times daily - NATO officials say the militants fled the region late last month. A shura - a council of village elders - was held in Garmser for the first time in years.

"Many of the people who have approached our patrols have told us how happy they are that the insurgents have left. They seem genuinely glad to be home," said Lt. Col. Anthony Henderson, the commanding officer of the MEU's infantry battalion.

Helmand province is the world's largest region for growing the opium poppy, the main ingredient in heroin.

The Marines arrived during the poppy harvest season, but didn't cut down the flowery plants. That would have alienated farmers with no other means of feeding their families, the Marines said. Most of the profits in the poppy trade go to traffickers, not farmers.

"Poppy fields in Afghanistan are [like] the cornfields of Ohio," said Staff Sgt. Jeremy Stover, 28, of Marion, Ohio. "When we got here they were asking us if it's OK to harvest poppy, and we said, 'Yeah, just don't use an AK-47.' "

British troops have responsibility for Helmand and maintain a small outpost on the northern tip of Garmser, but don't have enough soldiers to move farther south.

U.S. and British advisers hope to bring Afghan security forces into Garmser to capitalize on the Marines' gains, but the Afghan government probably does not have enough trained forces to move into Garmser either. That means the Taliban could move back in if the Marines leave.

The situation underlines why NATO commanders have called for NATO countries to contribute up to 10,000 more soldiers for Afghanistan.