This thesis examines the explanatory potential of Charles A. Kupchans hypotheses on cooperation and discord within defence alliances. The hypotheses are analysed in the context of Turkish non-alignment towards NATO’s open-door policy and the Swedish NATO-application. The thesis finds that the hypotheses partially explain Turkish non-cooperation but more importantly, it highlights the complex dynamics that shape decision making, cooperative and non-cooperative behaviour within NATO.  It shows that Türkiye’s pursuit of strategic autonomy and growing regional ambitions have been fuelled by increasing nationalist and anti-western domestic policies, leading to conflicts with other NATO members, resulting in sanctions and political isolation. Concessions regarding sanctions have been catalysts for Türkiye’s final ratification of the Swedish NATO-application.