Existing theories of international law are largely state-centric. While international cooperation can benefit all, states are often tempted to violate their promises in order to manage economic and political crises. States must accordingly balance enforcement against flexibility: legal institutions must provide enough enforcement that states comply most of the time yet also provide enough flexibility that states can violate during crises. Such a balance is possible when laws are crafted and enforced by unitary actors that will tolerate occasional violations by others in order to preserve their own right to occasionally violate. However, the changing doctrine of sovereign immunity has dramatically transformed the actual practice of international law. Non-state actors and domestic courts play an increasingly important role in challenging state legal violations, generating a divergence between the theory and practice of contemporary international law. This divergence is apparent in many issue areas, including terrorism, human rights, sovereign debt, and foreign investment. This divergence suggests that political scientists and legal scholars must reconsider the limits of state-centric theories and examine the role of non-state actors and domestic courts.