She studies the security of migration change. Her work focuses on new security challenges, including forced migrations, and how these may be used as a political weapon or a tool for diplomacy. Her recent book, “Weapons of Mass Migration: Forced Displacement, Coercion, and Foreign Policy,” won the 2011 International Studies Association’s Best Book of the Year award. Greenhill also was a co-author and co-editor with Peter Andreas of “Sex, Drugs, and Body Counts: The Politics of Numbers in Global Crime and Conflict.” She spoke with the Journal about her work and how she sees forced migrations playing out on today’s world stage.