The document discusses constructivism as an international relations theory and analyzes NATO enlargement through realist, liberalist, and constructivist lenses. It finds that constructivism best explains NATO's decision to enlarge by promoting shared Western liberal values like democracy and human rights through granting membership to Hungary, Poland, and Czech Republic, who had strongly internalized these norms. However, no single theory can fully account for international organizations; they must be combined to provide a comprehensive understanding.