The devastating effects of the war in Angola which resulted in damages estimated at $12 billion from 1975 to 1987, and had cost over 60,000 lives, as well as economic mismanagement led to a reassessment of Angola's diplomatic and economic options. Fidel Castro who was personally responsible for the Cuban involvement in Angola, and was involved in directing the operation in Angola, realized that the Angolan war was unwinnable. According to South African military sources, Luanda had prepared a new offensive against UNITA in southeast Angola in March 1987. As much as the battle of Mavinga had prompted South Africa to engage in the siege of Cuito Cuanavale, the Angolan-Cuban defeat at Mavinga led to a decisive reorientation of the Cuban military involvement. A breakthrough in the negotiations occurred during the third round of quadripartite talks in New York from 11 to 13 July 1988.