The trainer paced the grounds of a mountain enclave in southwestern Syria, shouting at dozens of new recruits as they drilled sprints between barricades made from old car tires.

“You have to practice as if it’s real,” screamed the instructor, Fadi Azam. “Want me to start shooting at you instead to make it real?” he said, lifting his rifle and firing a few rounds away from the group, the paw-paw-paw of gunfire echoing across the valley on a brisk morning in late January.

“You are lions, lions!” Mr. Azam yelled at the recruits, some of the tens of thousands of fighters from Syria’s Druse religious minority whose powerful militias control the rugged province of Sweida, southwest of the capital, Damascus. Sweida is the heartland of the Druse — a strategically important region bordering Jordan and near Israel — and these fighters stand to play a small but essential role in Syria’s future.

As the Islamist rebels who ousted the dictator Bashar al-Assad in December set up a new government, they are seeking to fold disparate militias including this one, which sprung up during Syria’s nearly 14-year civil war, into a single national force. A unified military is crucial to securing control over the entire country and establishing stability, but that goal has proved elusive.

Since January, several of the strongest Druse militias had been in talks with the government about their conditions for joining the new army. They were skeptical over the interim president’s pledges to protect the rights of Syria’s many religious and ethnic minorities.