<P> Relations between the steppe nomads and the settled people in and around Central Asia were marked by conflict . The nomadic lifestyle was well suited to warfare, and the steppe horse riders became some of the most militarily potent people in the world, due to the devastating techniques and ability of their horse archers . Periodically, tribal leaders or changing conditions would organise several tribes into a single military force, which would then often launch campaigns of conquest, especially into more' civilised' areas . A few of these types of tribal coalitions included the Huns' invasion of Europe, various Turkic migrations into Transoxiana, the Wu Hu attacks on China and most notably the Mongol conquest of much of Eurasia . </P> <P> The dominance of the nomads ended in the 16th century as firearms allowed settled people to gain control of the region . The Russian Empire, the Qing Dynasty of China, and other powers expanded into the area and seized the bulk of Central Asia by the end of the 19th century . After the Russian Revolution of 1917, the Soviet Union incorporated most of Central Asia; only Mongolia and Afghanistan remained nominally independent, although Mongolia existed as a Soviet satellite state and Soviet troops invaded Afghanistan in the late 20th century . The Soviet areas of Central Asia saw much industrialisation and construction of infrastructure, but also the suppression of local cultures and a lasting legacy of ethnic tensions and environmental problems . </P> <P> With the collapse of the Soviet Union in 1991, five Central Asian countries gained independence--Kazakhstan, Uzbekistan, Turkmenistan, Kyrgyzstan, and Tajikistan . In all of the new states, former Communist Party officials retained power as local strongmen . </P> <P> Recent genetic studies have concluded that modern humans (Homo sapiens) arrived in the region 40,000 to 50,000 years ago . As early as 4500 BC, small communities had developed permanent settlements and began to engage in agricultural practices as well as herding . Around this time, some of these communities began the domestication of the horse . Initially, the horses were bred solely for their meat, as a source of food . By 4000 BCE it is believed that they were used for transportation purposes; wheeled wagons began making an appearance during this time . </P>

When did the countries in central asia and the caucasus become independent