>> next, on american history tv, author and journalist howard blum describes german espionage in the u.s. with a focus on the years 1915 to 1917, before america entered world war i. in his book, "dark invasion 1915: germany's secret war and the hunt for the first terrorist cell in america," he details how german spies engaged in sabotage warfare ands a nation -- and assassination attempts. he also profiles tom tonni, who helped develop a modern counterterrorism strategy. this event was hosted by the new york military affairs symposium. it's about an hour. >> good evening and welcome! i am pleased to welcome howard blum an investigative journal journalist and author of the new york times best seller, "dark invasion," as well as many other great books. he is currently a contributing