sentences:  Charles' Polish ally, Stanisław Leszczyński, was facing internal problems of his own.Charles expected the support of a massive Cossack rebellion led by Mazepa in Ukraine, with estimates suggesting Mazepa of being able to muster some 40,000 troops, but the Russians subjugated the rebellion and destroyed its capital Baturin before the arrival of the Swedish troops.The harsh climate took its toll as well, as Charles marched his troops for winter camp in Ukraine.