The Republic of Türkiye was established as a result of the War of Independence, led by the military elite. The military struggle against the occupying Western powers, combined with concerns about their political aims, created fears, anxieties, and the so-called Sevres syndrome in the minds of the decision makers and public. This has influenced Türkiye’s security policies since 1923, leading to the dominance of a Realist perspective as one of the main characteristics of its foreign policy. This internal factor has been accompanied by external factors, including the conflicts in the southern, eastern, and northern neighborhoods over the last 100 years. The combination of historical factors, internal dynamics, and external circumstances has led to the emergence of state-led and hard power-dominated security policy. However, the Turkish leadership has occasionally implemented a more liberal approach to security, as seen during the Europeanization phase between 1999–2006, when a multilateral and cooperation-oriented security approach was adopted. This chapter explores the main internal and external factors affecting Türkiye’s security policies since the establishment of the Republic. It also sheds light on the continuities and changes in the Turkish leadership’s understanding of security.