Why did more than 15,000 people from the former Soviet bloc join ISIS - nearly a third of the group's foreign fighters? In Goodbye, ISIS: What Remains is Future, award-winning journalist Katerina Sergatskova investigates one of the most underexplored chapters of global terrorism. Drawing on years of reporting across Georgia, Turkey, Iraq, and Ukraine, she traces the personal stories of ISIS recruits, their families, and even those falsely accused of affiliation. Through vivid interviews and groundbreaking reporting, Sergatskova reveals how post-Soviet fighters shaped ISIS, how the movement spread into the Caucasus, and why Ukraine has become an unexpected landing place for some of its veterans. Alongside this narrative, she connects today's extremist networks to earlier figures like Dzhokhar Dudayev and Shamil Basayev, showing how past conflicts laid the groundwork for ISIS’s reach. Both deeply human and geopolitically urgent, Goodbye, ISIS challenges assumptions about terrorism, migration, and security in the post-Soviet world - and why understanding it matters for global stability.