By the late 18th century, much of the Cossack officer class in Ukraine was incorporated into the Russian nobility, but many of the rank and file Cossacks, including a substantial portion of the old Zaporozhians, were reduced to peasant status.
After the Treaty of Küçük Kaynarca, which annexed the Crimean Khanate into Russia, the need for further southern frontier defence (which the Zaporozhians carried out) no longer existed.