more than 80 percent of the agricultural plantations had been abandoned by their Portuguese owners; only 284 out of 692 factories continued to operate; more than 30,000 medium-level and high-level managers, technicians, and skilled workers had left the country; and 2,500 enterprises had been closed (75 percent of which had been abandoned by their owners). Furthermore, only 8,000 vehicles remained out of 153,000 registered, dozens of bridges had been destroyed, the trading network was disrupted, administrative services did not exist, and files and studies were missing. Angola's economic ills can also be traced to the legacy of Portuguese colonial development. Many of the white settlers had come to Angola after 1950 and were understandably quick to repatriate during the war of independence. During their stay, however, these settlers had appropriated Angolan lands, disrupting local peasant production of cash and subsistence crops. Moreover, Angola's industries depended on trade with Portugal—the colony's overwhelmingly dominant trade partner—for both markets and machinery. Only the petroleum and diamond industries boasted a wider clientele for investment and markets. Most important, the Portuguese had not trained Angolans to operate the larger industrial or agricultural enterprises, nor had they actively educated the population. Upon independence Angola thus found itself without markets or expertise to maintain even minimal economic growth. As a result, the government intervened, nationalizing most businesses and farms abandoned by the Portuguese. It established state farms to continue producing coffee, sugar, and sisal, and it took over the operations of all factories to maintain production. These attempts usually failed, primarily because of the lack of experienced managers and the continuing disruptions in rural areas caused by the UNITA insurgency. Only the petroleum sector continued to operate successfully, and by 1980 this sector had helped the gross domestic product reach US$3.6 billion, its highest level up to 1988. In the face of serious economic problems and the continuing war throughout the countryside, in 1987 the government announced plans to liberalize economic policies and promote private investment and involvement in the economy. 1990s United Nations Angola Verification Mission III and MONUA spent US$1.5 billion overseeing implementation of the Lusaka Protocol, a 1994 peace accord that ultimately failed to end the civil war. The protocol prohibited UNITA from buying foreign arms, a provision the United Nations largely did not enforce, so both sides continued to build up their stockpile. UNITA purchased weapons in 1996 and 1997 from private sources