The Most Infamous Terrorist Groups of the 21st Century: The History of the Organizations Behind This Century's Deadliest Attacks

Since the attacks on September 11, 2001, the world has struggled to define al-Qaeda, an amorphous, growing, and seemingly inexhaustible organization. Once a relatively organized group based in one country with a defined hierarchy and clear leadership, al-Qaeda has transformed into a transnational phenomenon over the last few decades, with branches and affiliates operating in dozens of countries across the world. Many call al-Qaeda an enemy, while some define it as an ideology, and others an...