As the world prepares to mark the anniversary of the 9/11 attacks two decades on, we discuss the history of plane hijackings. From politically motivated attacks to propaganda tools used by governments, Dr Yannick Veilleux-Lepage shares his knowledge of the broader context of the attacks of 2001. Dr. Yannick Veilleux-Lepage is assistant Professor of Terrorism and Political Violence at the Institute of Security and Global Affairs at Leiden University. His book, 'How Terror Evolves: The Emergence and Spread of Terrorist Techniques' is published by Rowman & Littlefield.