Formed from the merger of the British colony of the Gold Coast and the Togoland trust territory, in 1957, Ghana became the first sub-Saharan country in colonial Africa to gain its independence. In the years following independence, Ghana endured a period of political instability arising from corruption and mismanagement.  In 1960, a new constitution changed Ghana from the parliamentary system to a republican form of government headed by a powerful president. In 1966 the president was deposed in a coup, heralding years of mostly-military rule. In 1981, Flight Lieutenant Jerry Rawlings staged a second coup. He was formally elected president in 1992 when a constitution allowing for a multi-party system was approved in a referendum, ushering in a period of democracy. Ghana is rich in natural resources such as gold, diamonds, timber, and cocoa. Agriculture has traditionally been, and continues to be, the mainstay of the economy, with cocoa beans and cocoa products remaining dominant for exports. The discovery of major offshore oil reserves was announced in June 2007, and oil production is expected to start in 2011, which will likely bolster growth and fiscal revenues.