For months, U.S. military officials had been vetting the first unit of Syrian fighters slated to join a new force to be trained by the United States and allied nations. But when violence flared up in the unit’s home area, the fighters made a decision to stay home and defend their communities, forcing U.S military officials to line up an alternate unit.

That last-minute scramble delayed the launch of the training program by several weeks to some time in May, according to military officials. It is also a sign of the obstacles the United States and its allies face as they try to build a rebel force, from a distance, in the midst of Syria’s civil war.

A senior military official said that training preparations had been held up “due to the fluid environment in Syria” but were now moving ahead. Training sites will eventually be opened in Turkey, Saudi Arabia, Qatar and Jordan. […]