Russia’s private army

A clear chain of command that follows rules of war. These are fundamental principles in a modern military. But increasingly, traditional armies are getting competition for another kind of fighting force — mercenaries.  This week on The World, we’re featuring reporting about global threats that are slipping under the radar, thanks to our friends at the national security podcast “Things That Go Boom.” Laicie Heeley reports on the shadows of Russia’s army, and new questions for the US military.