What are the ethnic and social roots of the Cossacks?

Theories of the origin of the Cossacks in Zaporozhye still cause heated discussions among researchers. Back in the era of romanticism, “Cossack chroniclers” Samoil Velichko and Grigory Grabyanka put forward the thesis of the Khazar origin of the Cossacks. Ideas were put forward that the Cossacks were formed from fugitive and poor peasants. Some theories say that the Polish gentry core became the social basis for the formation of the Cossacks. which guarded the borders of Poland. Theories of the origin of the Cossacks from the roamers also arose.