El Salvador's economy has historically been dominated by agriculture, beginning with the Spanish taking control of the indigenous cacao crop in the 16th century, with production centered in Izalco, and the use of balsam from the ranges of La Libertad and Ahuachapan. This was followed by a boom in use of the indigo plant (''añil'' in Spanish) in the 19th century, mainly for its use as a dye. Thereafter the focus shifted to coffee, which by the early 20th century accounted for 90% of export earnings. El Salvador has since reduced its dependence on coffee and embarked on diversifying its economy by opening up trade and financial links and expanding the manufacturing sector. The colón, the currency of El Salvador since 1892, was replaced by the United States dollar in 2001. 