This lecture discusses three key concepts from realist international relations theory: anarchy, the security dilemma, and problems of credible commitment. It defines anarchy as the lack of a world government over sovereign states. Anarchy leads to two problems - the security dilemma, where actions by one state to increase security can paradoxically decrease security for others, and problems of credible commitment, where states cannot believably promise not to act in their self-interest without enforcement. The lecture also notes that while realists see these as major constraints of the international system, liberal theorists argue anarchy is less constraining than realists claim.