Before 9/11, before Pearl Harbor, another unsuspected foreign attack on the United States shocked the nation and forever altered the course of history. In 1916, Pancho Villa, a guerrilla fighter who commanded an ever-changing force of conscripts in northern Mexico, attached a border town in New Mexico. It was a raid that angered Americans, and President Woodrow Wilson ordered the Punitive Expedition in which the US Army invaded Mexico and defeated General Villa's troops, but failed to capture him. This event may have been the catalyst for America’s entry into World War One and permanently altered U.S.-Mexican border policy. Jeff Guinn, author of the new book "War on the Border," joins us to discuss this critically important event in American history. The “Punitive Expedition” was launched in retaliation under Pershing’s command and brought together the Army, National Guard, and the Texas Rangers—who were little more than organized vigilantes.   The American expedition was the last action by the legendary African-American “Buffalo Soldiers.” It was also the first time the Army used automobiles and trucks, which were of limited value in Mexico, a country with no paved roads or gas stations. Curtiss Jenny airplanes did reconnaissance, another first. One era of warfare was coming to a close as another was beginning. But despite some bloody encounters, the Punitive Expedition eventually withdrew without capturing Villa. Although the bloodshed has ended, the US-Mexico border remains as vexed and volatile an issue as ever.