Peter expected that king Charles of Sweden was going to attack and thought that he could spare no forces. In the opinion of Mazepa, this blatantly violated the Treaty of Pereyaslav, since Russia refused to protect Ukraine's territory and left it to fare on its own. As the Swedish and Polish armies advanced towards Ukraine, Mazepa allied with them on 28 October 1708. However, only 3,000 Cossacks followed their Hetman, with the rest remaining loyal to the Tsar.
It was from that moment that King Charles XII of Sweden granted Mazepa the right to use the colors of the Swedish military bandera (yellow and blue) as the insignia of the Cossack detachments led by Mazepa, later these would be the colors of the Flag of Ukraine.