While both countries were shaken by internal strife, many smaller factions thrived. Polish Lisowczycy mercenaries, who were essential in the defense of Smolensk in 1612, when most regulars (wojsko kwarciane) mutinied and joined the "konfederacja rohatynska", were content to guard the Polish border against the Russian incursions for the next three years. However, in 1615 Aleksander Józef Lisowski gathered many outlaws and invaded Russia with 6 "chorągiew" of cavalry. He besieged Bryansk and defeated the relief force of a few thousand soldiers under Prince Yuri Shakhovskoy near Karachev. Then Lisowski defeated the front guard of a force several times larger than his own, under the command of knyaz Dmitry Pozharsky, who decided to defend instead of attack and fortified his forces in a camp. Lisowczycy broke contact with his forces, burned Belyov and Likhvin, took Peremyshl, turned north, defeated the Russian army at Rzhev, proceeded north towards Kashin, burned Torzhok, and returned to Poland heavy with loot without any further opposition from Russian forces. Lisowski and his forces remained at the Russo–Polish border until autumn 1616, at which point Lisowski suddenly fell ill and died on 11 October. The formation was then known as "Lisowczycy". Despite the death of Lisowski, his forces remained a significant threat: in 1616 they captured Kursk and defeated Russian forces at Bolkhov.