Cultures in the region have been dated back to at least the fourth millennium BC, including the Bronze Age Bactria–Margiana Archaeological Complex, the Andronovo cultures and the pro-urban site of Sarazm, a UNESCO World Heritage Site.[31] The earliest recorded history of the region dates back to about 500 BC when most, if not all, of Tajikistan was part of the Achaemenid Empire.[23] Some authors have suggested that in the seventh and sixth centuries BC parts of Tajikistan, including territories in the Zeravshan valley, formed part of the Hindu Kambojas tribe[32][33] before it became part of the Achaemenid Empire.[34] After the region's conquest by Alexander the Great it became part of the Greco-Bactrian Kingdom, a successor state of Alexander's empire. Northern Tajikistan (the cities of Khujand and Panjakent) was part of Sogdia, a collection of city-states which was overrun by Scytho-Siberians and Yuezhi nomadic tribes around 150 BC. The Silk Road passed through the region and following the expedition of Chinese explorer Zhang Qian during the reign of Wudi (141 BC–87 BC) commercial relations between Han Empire and Sogdiana flourished.[35][36] Sogdians played a role in facilitating trade and worked in other capacities, as farmers, carpetweavers, glassmakers, and woodcarvers.[37] The Kushan Empire, a collection of Yuezhi tribes, took control of the region in the first century AD and ruled until the fourth century AD during which time Buddhism, Nestorian Christianity, Zoroastrianism, and Manichaeism were practised in the region.[38] Later the Hephthalite Empire, a collection of nomadic tribes, moved into the region, and the Arabs disseminated Islam in the eighth century.[38] The Samanid ruler Mansur I (961–976) 19th-century painting of lake Zorkul and a local Tajik inhabitant Samanid Empire[edit] Main article: Samanid Empire The Samanid Empire, 819 to 999, restored Persian control of the region and enlarged the cities of Samarkand and Bukhara, which became the cultural centers of Iran; the region was known as Khorasan. The empire was centered in Khorasan and Transoxiana; at its greatest extent encompassing Afghanistan, parts of Iran, Tajikistan, Turkmenistan, Uzbekistan, Kyrgyzstan, parts of Kazakhstan, and Pakistan. Four brothers Nuh, Ahmad, Yahya, and Ilyas founded the Samanid state. Each of them ruled territory under Abbasid suzerainty. In 892, Ismail Samani (892–907) united the Samanid state under one ruler, thus putting an end to the feudal system used by the Samanids. It was under him that the Samanids became independent of Abbasid authority. The Kara-Khanid Khanate conquered Transoxania (which corresponded approximately with what later would be Uzbekistan, Tajikistan, southern Kyrgyzstan, and southwest Kazakhstan) and ruled between 999 and 1211.[39][40] Their arrival in Transoxania signalled a definitive shift from Iranian to Turkic predominance in Central Asia,[41] and gradually the Kara-khanids became assimilated into the Perso-Arab Muslim culture of the region.[42] In the 13th century, the Mongol Empire swept through Central Asia, invaded the Khwarezmian Empire and sacked its cities, looting and massacring people. Turco-Mongol conqueror Tamerlane founded the Timurid Empire, becoming the first ruler of the Timurid dynasty in and around what later became Tajikistan and Central Asia.[43] Bukharan rule[edit] Main article: Khanate of Bukhara What later became Tajikistan fell under the rule of the Khanate of Bukhara during the 16th century and, with the empire's collapse in the 18th century, it came under the rule of the Emirate of Bukhara and Khanate of Kokand. The Emirate of Bukhara remained intact until the 20th century. Imperial Russia[edit] Main article: Russian conquest of Turkestan Further information: Russian Turkestan and The Great Game During the 19th century, the Russian Empire began to conquer parts of the region.[44] Russian Imperialism led to the Russian Empire's conquest of Central Asia during the 19th century's Imperial Era. Between 1864 and 1885, Russia gradually took control of the entire territory of Russian Turkestan, the Tajikistan portion of which had been controlled by the Emirate of Bukhara and Khanate of Kokand. Russia was interested in gaining access to a supply of cotton and in the 1870s attempted to switch cultivation in the region from grain to cotton (a strategy later copied and expanded by the Soviets).[45] During the 19th century, the Jadidists established themselves as an Islamic social movement throughout the region. While the Jadidists were pro-modernization and not necessarily anti-Russian, the Russians viewed the movement as a threat because the Russian Empire was predominantly Christian.[46] Russian troops were required to restore order during uprisings against the Khanate of Kokand between 1910 and 1913. Further violence occurred in July 1916 when demonstrators attacked Russian soldiers in Khujand over the threat of forced conscription during World War I. While Russian troops brought Khujand back under control, clashes continued throughout the year in various locations in Tajikistan. [47] Soviet period[edit] Main articles: Basmachi movement and Tajik Soviet Socialist Republic Soviet negotiations with basmachi, 1921 After the Russian Revolution of 1917 guerrillas throughout Central Asia, known as basmachi, waged a war against Bolshevik armies in an attempt to maintain independence.[43] The Bolsheviks prevailed after a four-year war, in which mosques and villages were burned down and the population suppressed. Between 1928 and 1941, Soviet authorities started an anti-religious campaign of secularization. Practising Christianity, Islam, or Judaism was discouraged and repressed; due to the Soviet anti-religious legislation, several churches, mosques, and synagogues were closed.[48] As a consequence of the conflict and Soviet agriculture policies, Central Asia, Tajikistan included, underwent a famine that claimed lives.[49] In 1924, the Tajik Autonomous Soviet Socialist Republic was created as a part of Uzbekistan,[43] and in 1929 the Tajikistan Soviet Socialist Republic (Tajikistan SSR, Таджикская ССР) was made a separate constituent republic;[43] the predominantly ethnic Tajik cities of Samarkand and Bukhara remained in the Uzbek SSR. Between 1927 and 1934, collectivization of agriculture and an expansion of cotton production took place, especially in the southern region.