Throughout the history of Vietnam, its economy has been based largely on agriculture—primarily wet rice cultivation. Bauxite, an important material in the production of aluminium, is mined in central Vietnam. Since reunification, the country's economy is shaped primarily by the CPV through Five Year Plans decided upon at the plenary sessions of the Central Committee and national congresses. The collectivisation of farms, factories, and capital goods was carried out as part of the establishment of central planning, with millions of people working for state enterprises. Under strict state control, Vietnam's economy continued to be plagued by inefficiency, corruption in state-owned enterprises, poor quality and underproduction. With the decline in economic aid from its main trading partner, the Soviet Union, following the erosion of the Eastern bloc in the late 1980s, and the subsequent collapse of the Soviet Union, as well as the negative impacts of the post-war trade embargo imposed by the United States, Vietnam began to liberalise its trade by devaluing its exchange rate to increase exports and embarked on a policy of economic development.