South African tactics became increasingly aggressive as the conflict progressed. The SADF's incursions produced Angolan casualties and occasionally resulted in severe collateral damage to economic installations regarded as vital to the Angolan economy. Ostensibly to stop these raids, but also to disrupt the growing alliance between the SADF and the National Union for the Total Independence for Angola (UNITA), which the former was arming with captured PLAN equipment, the Soviet Union backed the People's Armed Forces of Liberation of Angola (FAPLA) through a large contingent of military advisers and up to four billion dollars' worth of modern defence technology in the 1980s. Beginning in 1984, regular Angolan units under Soviet command were confident enough to confront the SADF. Their positions were also bolstered by thousands of Cuban troops. The state of war between South Africa and Angola briefly ended with the short-lived Lusaka Accords, but resumed in August 1985 as both PLAN and UNITA took advantage of the ceasefire to intensify their own guerrilla activity, leading to a renewed phase of FAPLA combat operations culminating in the Battle of Cuito Cuanavale. The South African Border War was virtually ended by the Tripartite Accord, mediated by the United States, which committed to a withdrawal of Cuban and South African military personnel from Angola and South West Africa, respectively. PLAN launched its final guerrilla campaign in April 1989. South West Africa received formal independence as the Republic of Namibia a year later, on 21 March 1990.