A cornerstone of the expanded U.S. military campaign against Islamic State militants will be reliance on U.S.-trained local forces to confront the group head on.

But the U.S. has a poor track record of taking or keeping control in areas such as Iraq and Libya for extended periods, experiences that underscore the risks of depending on moderate rebels in Syria and state security forces in Iraq.

Relying on local forces and eschewing the use of American combat troops has become a favorite strategy of President Barack Obama as a way to reduce the risk of being dragged into a protracted foreign conflict. But some defense officials and experts say that approach also can heighten the risk of failure. […]