Turkey's Syria policy after 2011 and its effect on Türkiye-USA relations

This thesis analyzes Turkey's cross-border security policies towards Syria after 2011 and examines the impact of these policies on Turkey–U.S. relations. The study focuses onfive major military operations — Shah Euphrates, Operation Euphrates Shield,Operation Olive Branch, Operation Peace Spring, and Operation Spring Shield — conducted between 2011 and 2020, evaluating their justifications, strategic objectives, and diplomatic consequences within a chronological framework. The research systematically explores the transformation of Turkey's border security policies and the U.S. responses to these operations. In this context, U.S. reactions were analyzed through official statements, diplomatic documents, parliamentary records, international reports, think-tank analyses, and media coverage, providing a comprehensive understanding of bilateral dynamics. A qualitative research design was adopted, utilizing document analysis as the primary data collection method and qualitative content analysis for data interpretation. Data were coded and analyzed thematically within a theoretical framework that combines Realism/Neorealism, the Copenhagen School's Securitization Theory, and Institutionalism. These theories were employed to explain Turkey's policies through the lenses of power politics, threat construction, and institutional mechanisms, enabling a multi- layered analysis of state behavior and alliance dynamics. The findings indicate that Turkey's cross-border operations contributed to a partial improvement in border security. However, the U.S. military and political support for the PYD/YPG caused a deep crisis of trust within the alliance, leading to a deterioration in Turkey–U.S. relations. Furthermore, the research reveals the limited effectiveness of NATO mechanisms in managing this alliance crisis. By presenting a detailed, chronological, and multi-theoretical analysis, this study fills a significant gap in the literature and provides valuable insights for both scholars and policymakers working on international relations and security studies. Keywords: Cross-Border Operation, Security Policy, Realism, Securitization, Institutionalism