This book is based on the master’s thesis that I defended in 2020. Foreign fighters and returning foreign fighters are among the most important security issues that the Middle East and Europe is facing today. Moreover, the significance level of this issue is increasing day by day.

After I read the PhD thesis of David Malet, which is about the classification of foreign fighters, I became interested in this topic. After reading about the topic I realized that most of the academic articles and reports on foreign fighters focus on Islamist/jihadi groups while secular and leftist organizations are largely neglected by scholars and researchers. So I eventually decided to study the classification of foreign YPG fighters to focus on this neglected area of research.

I would like to express my gratitude to my supervisor, Prof. Mehmet Şahin who guided me throughout this study.

I wish to thank the members of my thesis committee: Prof. Türel Yılmaz Şahin and Dr. Mehmet Levent Yılmaz.

I would also like to thank Assoc. Prof. Murat Yeşiltaş who inspired me to choose this topic for my dissertation.

Finally, I must express my gratitude to my family and friends for providing me with unfailing support and continuous encouragement throughout my years of study and through the process of researching and writing this thesis.