More Russian speakers appeared in the northern, central and eastern territories that are now 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 Slobozhanschyna 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 parts which were under the Cossack Hetmanate (a predecessor of modern Ukraine entered the Russian Tsardom. This brought significant, but still small, wave of Russian settlers into what is now central Ukraine (primarily several thousand soldiers stationed in garrisons, out of a population of approximately 1.2 million non-Russians).