In a different part of southeastern Europe, on the middle Dnieper in what is now Ukraine, lived the Zaporozhian Cossacks. By the late 18th century, however, their combat ability was greatly reduced. With their traditional adversaries, the Crimean Khanate and the Polish–Lithuanian Commonwealth now all but defunct, the Russian administration saw little military use for them. The Zaporozhian Sich, however, represented a safe haven for runaway serfs, where the state authority did not extend, and often took part in rebellions which were constantly breaking out in Ukraine. Another problem for the imperial Russian government was the Cossacks' resistance to colonization of lands the government considered theirs. In 1775, after numerous attacks on Serbian colonisers, the Russian Empress Catherine the Great had Grigory Potemkin destroy the Zaporozhian Host. The operation was carried out by General Pyotr Tekeli.