More Russian speakers appeared in the northern, central and eastern territories of modern Ukraine during the late 17th century, following the Cossack Rebellion (1648–1657) which Bohdan Khmelnytsky led against Poland. The Khmelnytsky Uprising led to a massive movement of Ukrainian settlers to the Slobozhanshchyna region, which converted it from a sparsely inhabited frontier area to one of the major populated regions of the Tsardom of Russia. Following the Pereyaslav Rada of 1654 the modern northern and eastern parts of Ukraine came under the hegemony of the Russian Tsardom. This brought the first significant, but still small, wave of Russian settlers into central Ukraine (primarily several thousand soldiers stationed in garrisons, out of a population of approximately 1.2 million non-Russians). Although the number of Russian settlers in Ukraine prior to the 18th century remained small, the local upper-classes within the part of Ukraine acquired by Russia came to use the Russian language widely.