Tajikistan is a landlocked, mountainous country in central Asia. Arabs brought Islam to the region between the seventh and eighth centuries. Tajikistan came under Russian control during the late 19th century. The country became an autonomous republic within the Soviet Union in 1924 and an independent Soviet Socialist Republic in 1929. Following the breakup of the Soviet Union, Tajikistan became independent in 1991, but soon fell into a civil war in 1992. The five-year civil war between the Moscow-backed government and the Islamist-led opposition ended in 1997 with a United Nations-brokered peace agreement. Tajikistan has one of the lowest per capita GDPs (about US$700 in 2009) among the 15 former Soviet republics, and is one of the poorest countries in the world. Its economic activity is highly dependent on exports of cotton and aluminum, making the economy extremely vulnerable to external shocks. The country has significant development potential in the hydroelectric power sector, but much of this potential remains unexploited because of an uncertain private investment environment and a protracted structural reform process.