Reassurance and Resolve: Enhancing U.S. Extended Deterrence Credibility in Europe

In the modern international security environment, extended deterrence and assurance remain critical components to the deterrence of the North Atlantic Treaty Organization’s (NATO’s) competitors and threats. Within this organization, the United States plays a crucial role as the major nuclear power that supplies extended nuclear deterrence to its NATO allies. To enhance the credibility of its extended deterrence commitments, the U.S. practices various forms of assurance for its allies. This paper examines the extended deterrence relationships between the U.S. and France, Germany, and Estonia. It analyzes what assurance tools and strategies have been advantageous, disadvantageous, or irrelevant to the credibility of the United States’ extended deterrence commitments and capabilities. This paper uses three theories on assurance and alliances, the Healy Theorem, Balance-of-Threat Theory, and Costly Signaling Theory, to evaluate the various U.S. assurance efforts for these three European allies. Following the three case studies, the factors that contributed to the success or failure of these U.S. assurance relationships are discussed, and the implications of these findings on future U.S. assurance policies and strategies are considered in a recommendations section. This paper reveals that allies have unique needs and require tailored assurance strategies that incorporate various physical demonstrations of commitment and capability, transparent and consistent communication, and a willingness to respond to new threats and concerns.