Newly disclosed government documents show that U.S. Secretary of State Henry Kissinger drew up plans to “smash Cuba” with air strikes nearly 40 years ago, in response to Cuban President Fidel Castro’s 1976 military intervention in Angola and the small country’s pursuit of its own foreign policy in Africa.

The documents are posted online and will be published this month in Back Channel to Cuba by longtime Cuba experts William M. LeoGrande, a professor of government at American University, and Peter Kornbluh, the director of the National Security Archive’s Cuba Documentation Project.

They reveal that Kissinger was “extremely apoplectic” that Castro passed up a chance to normalize relations with the United States in favor of potentially expanding Cuba’s presence in Africa, Kornbluh told the New York Times. In late 1975, Castro sent troops to Angola to help the newly independent nation fend off attacks from South Africa and right-wing guerrillas—which Kissinger feared could disrupt his own plans on the African continent.