Miller served in the military from 1983 to 2014. He started as an enlisted soldier, then was commissioned as a second lieutenant in 1987, and then joined the United States Army Special Forces in 1993.
He received a Master of Arts in national security studies from the Naval War College in 2001. He also graduated from the College of Naval Command and Staff and the Army War College.
He participated in wars in Afghanistan and Iraq. In Afghanistan, he was a company commander in the 5th Special Forces Group, which fought al-Qaeda and the Taliban. In Iraq, he commanded Special Forces units in 2006 and 2007. His promotion to colonel was approved in December 2009.
Miller served as program executive officer (PEO) for rotary wing programs at U.S. Special Operations Command in 2010. One of his last assignments as an Army officer was as Director for Special Operations and Irregular Warfare in the Office of the Assistant Secretary of Defense for Special Operations/Low-Intensity Conflict & Interdependent Capabilities at the Pentagon in 2011.
Never forget the military is still a bureaucracy and you can get a long way in any bureaucracy by just parroting the groupthink.