Shein's army retreated to its main camp, which was in turn surrounded by Commonwealth forces in mid-October. The besieged Russians waited for relief, but none arrived, as Commonwealth and Cossack cavalry had been sent to disrupt the Russian rear. Some historians also cite dissent and internal divisions in the Russian camp as responsible for their inaction and ineffectiveness. (Jasienica blames the Russian warlords, and Parker the foreign mercenaries.) The Tatar invasion threatening the south Russian borderlands was a contributory factor, with many soldiers and boyars from those regions deserting the Russian camp to return to protect their homeland. Some foreign mercenaries also deserted to the Commonwealth side.