 In the meantime, the real numbers of Cossacks swelled by the constant flow of runaway peasants and, especially, at the end of the Polish-Swedish War (1625–1629), by the addition of a huge number of demobilized Ukrainians who refused to accept a return under Polish serfdom.The ranks of Cossacks who joined the resistance reached forty thousand.The Cossack uprising fell on the fertile ground of the overall condition of Ukrainian peasantry who under Polish control were subject to continued enserfment and exploitation by mostly Polish or polonized szlachta (nobility).