Please answer the following question: Given the following passage  "Russian Imperialism led to the Russian Empire's conquest of Central Asia during the late 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).[citation needed] By 1885 Tajikistan's territory was either ruled by the Russian Empire or its vassal state, the Emirate of Bukhara, nevertheless Tajiks felt little Russian influence.[citation needed]",  answer the following question. Note that the answer is present within the text.  Question: What preceded the taking of the Tajikistan portion?
Answer:
Russian Imperialism