This analysis is about a country’s choice of cooperation over non-cooperation on building national defense. It argues that states opt for alternative strategies when they realize that they can no longer depend on the hegemon for their national defense. Turkey’s deal for the S-400 missile defense system with Russia and the European Union’s Permanent Structured Cooperation (PESCO), which aims to intensify the union’s internal defense cooperation, are clear cases of strategic non-cooperation. This analysis will show that although the United States was a security partner of both the EU and Turkey when it decided to no longer commit to responding to its allies’ security concerns, the latter took over the responsibility of ensuring their national defenses.