More Russian speakers appeared in northern, central and eastern Ukrainian territories during the late 17th century, following the Cossack Rebellion led by Bohdan Khmelnytsky. The Uprising led to a massive movement of Ukrainian settlers to the Sloboda Ukraine region, which converted it from a sparsely inhabited frontier area to one of the major populated regions of the Tsardom of Russia. Following the Treaty of Pereyaslav, Ukrainian Cossacks lands, including the modern northern and eastern parts of Ukraine became a protectorate of the into the Tsardom of Russia. 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).