The United States has maintained a policy of strategic ambiguity toward Taiwan for more than four decades. It does not formally recognize Taiwan as an independent state. It does not provide a treaty guarantee equivalent to the commitments it has made to Japan, South Korea, or NATO allies. It does sell Taiwan defensive weapons under the Taiwan Relations Act, and it maintains unofficial relations through the American Institute in Taiwan. What it has not done is say explicitly and publicly whether it would use military force to defend Taiwan against a Chinese attack. This ambiguity has been the foundation of American cross-strait policy since 1979, and it has been under increasing strain as the military balance in the strait has shifted.