What is now Ecuador formed part of the northern Inca Empire until the Spanish arrived and gained control in the 1530s. After Spain lost control of Ecuador in 1822, Ecuador joined Simon Bolivar's Republic of Gran Colombia, only to become a separate republic in 1830. The years following independence were marked by instability with a rapid succession of rulers, including a coup in 1925. Following World War II, agricultural development brought prosperity and peace, and the country enjoyed a decade of stability and democracy. However, political turbulence returned in the 1960s, followed by a period of military dictatorship between 1972 and 1979. The 1980s and the beginning of the 1990s saw a period of democracy, but instability returned with three presidents having been ousted since 1997. In September 2008, voters approved a new constitution - Ecuador's twentieth since gaining independence. The new constitutional framework enabled President Correa to win a second term in April 2009. Endowed with substantial petroleum resources, Ecuador’s economy is dominated by the oil industry, but the economy is vulnerable to external shocks such as fluctuations in world oil prices and other commodity prices.