One of the fastest growing—and underreported—subjects in international relations is the rise of private armies. Dr. Sean McFate, Atlantic Council senior fellow and former private military contractor, joins "Doorstep" co-hosts Nick Gvosdev and Tatiana Serafin to discuss his book "The New Rules of War" and how our current paradigm of warfare is obsolete. How can America rethink the trillions of dollars spent on defense? Is the risk of inaction creating a new "Middle Ages"?