<P> The roças system, which gave the plantation managers a high degree of authority, led to abuses against the African farm workers . Although Portugal officially abolished slavery in 1876, the practice of forced paid labor continued . In the early 20th century, an internationally publicized controversy arose over charges that Angolan contract workers were being subjected to forced labor and unsatisfactory working conditions . Sporadic labor unrest and dissatisfaction continued well into the 20th century, culminating in an outbreak of riots in 1953 in which several hundred African laborers were killed in a clash with their Portuguese rulers . This "Batepá Massacre" remains a major event in the colonial history of the islands, and its anniversary is officially observed by the government . </P> <P> During the 1967--70 secession war from Nigeria (Nigerian Civil War), São Tomé served as the major base of operations for the Biafran airlift . The airlift was an international humanitarian relief effort (the largest civilian airlift to date) that transported food and medicine to eastern Nigeria . It is estimated to have saved more than a million lives . </P> <P> By the late 1950s, when other emerging nations across the African Continent were demanding independence, a small group of São Toméans had formed the Movement for the Liberation of São Tomé and Príncipe (MLSTP), which eventually established its base in nearby Gabon . Picking up momentum in the 1960s, events moved quickly after the overthrow of the Caetano dictatorship in Portugal in April 1974 . The new Portuguese regime was committed to the dissolution of its overseas colonies; in November 1974, their representatives met with the MLSTP in Algiers and worked out an agreement for the transfer of sovereignty . After a period of transitional government, São Tomé and Príncipe achieved independence on July 12, 1975, choosing as its first president the MLSTP Secretary General Manuel Pinto da Costa . </P> <P> In 1990, São Tomé became one of the first African countries to embrace democratic reform and changes to the constitution--the legalization of opposition political parties--led to elections in 1991 that were nonviolent, free, and transparent . Miguel Trovoada, a former prime minister who had been in exile since 1986, returned as an independent candidate and was elected president . Trovoada was re-elected in São Tomé's second multiparty presidential election in 1996 . The Party of Democratic Convergence (PCD) toppled the MLSTP to take a majority of seats in the National Assembly, with the MLSTP becoming an important and vocal minority party . Municipal elections followed in late 1992, in which the MLSTP came back to win a majority of seats on five of seven regional councils . In early legislative elections in October 1994, the MLSTP won a plurality of seats in the Assembly . It regained an outright majority of seats in the November 1998 elections . The Government of São Tomé fully functions under a multiparty system . Presidential elections were held in July 2001 . The candidate backed by the Independent Democratic Action party, Fradique de Menezes, was elected in the first round and inaugurated on September 3 . Parliamentary elections were held in March 2002 . For the next four years, a series of short - lived, opposition - led governments were formed . </P>

When did sao tome and principe gain independence