The fall of Afghanistan raises serious questions about whether the United States and the West more broadly are able to successfully implement what military practitioners call Foreign Internal Defense, or supporting a friendly foreign government under attack from an internal insurgency. What explains success or failure in these cases? SSI Live host Dr. John R. Deni invited his SSI colleagues Dr. Chris Mason to address the key variables Washington needs to bear in mind when it considers whether to intervene abroad. Dr. Mason drew on his long experience working in and studying Afghanistan, his book The Strategic Lessons Unlearned from Vietnam, Iraq, and Afghanistan, and his recent Parameters article on how “Counterinsurgency Doctrine is Wrong.”