Turkmenistan, a desert nation, has the second lowest population density (after Kazakhstan) in former Soviet Central Asia. Nomadic herdsmen for centuries, Turkmen were subdued by Russia during the late 19th century, gaining independence in 1991. Begun in the 1950s, the Garagum Canal, one of the world's longest, drained water away from the Amu Darya River to southern Turkmenistan—but the old canal leaks and creates salt deserts. Also, by diverting water from the Amu Darya, the canal contributed greatly to the drying up of the Aral Sea. Turkmenistan's hope lies in its sector of the Caspian Sea, where oil and natural gas fields are concentrated. The country's natural gas reserves rank fifth in the world—but development of gas exports is hampered by a lack of gas-pipeline routes out of landlocked Turkmenistan. Russia controls most of the pipelines and has refused to export Turkmen natural gas to hard-currency markets. A gas pipeline through Afghanistan to Pakistan gained approval in 2002, but the security situation in Afghanistan remains an obstacle. Disputes between Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan over Caspian Sea seabed and maritime boundaries limits international investment in new gas fields and pipelines. Revenue from oil and gas production benefits few because of an authoritarian and corrupt government.