The Cossacks (Russian: Каза́ки́, Kazaki; Ukrainian: Козаки́, Kozaky; also known as Polish: Kozacy, originally derived from Turkic Qazaqlar) are a traditional community of martial people living in the southern steppe regions of Eastern Europe and Asia. The Cossacks themselves make up a Cossack host, which allows to distinguish individual Cossack groups by their location, history, traditions and even military roles.

Although several theories exist on the formation of Cossacks, towards the end of the 14th century two Cossack hosts emerged — the Zaporozhian Host located in the lower Dnieper River and the Don Host located on the Don River. The Zaporozhian Sich joined by numerous serfs fleeing from Ukraine and other territories swelled into a powerful military force and led a rebellion against Polish domination in Ukraine. Under the leadership of a Cossack hetman Bohdan Khmelnytsky a Cossack Hetmanate was formed in 1649. Its prominence and the role of the Zaporozhian Cossacks began to diminish after the Treaty of Pereyaslavl with the Tsardom of Russia. The Cossack Hetmanate in Ukraine was abolished in 1764 and the Zaporozhian Sich was finally destroyed by the Russian army in 1775. Centuries later the Zaporozhian Cossacks would be viewed as progenitors of the modern Ukrainian nation.

The Don Cossack Host allied with the Tsardom of Russia since the 16th century began a systematic conquest of conquering and colonizing lands to secure her borders on the Volga, the whole of Siberia, the Yaik and the Terek Rivers, where newer Cossack hosts formed. By the end of the 18th century, the Cossacks were a special social estate (sosloviye) that served as border guards on national and internal ethnic borders as was in the case of the Caucasus War, would regularly supplied men to any conflict such as the numerous Russo-Turkish Wars. In return they enjoyed a vast social autonomy. This caused them to form a stereotypical portrayal of 19th century Russian Empire and its government abroad and domestically.

During the Russian Civil War Cossack regions became the main centres for the Anti-Bolshevik White movement, a portion of whom would form the White Emigre. At the hands of the Red Army and after its victory, the Cossack lands were subjected to famine, and suffered extensive repressions that were relaxed only in the mid-1930s. During the Second World War Cossacks fought for both the Soviet Union and collaborated with Nazi Germany. After the Collapse of the Soviet Union, Cossack lifestyle blossomed in Russia. Many fought in Post-Soviet Conflicts and there are special units in the Russian Military wholly made of them. Cossacks also have a parallel civil administration and police duties in their homelands and are now an integral part of the Russian society. There are also Cossack organizations in Kazakhstan, Ukraine and other countries.

The Cossacks (Russian: Каза́ки́, Kazaki; Ukrainian: Козаки́, Kozaky; also known as Polish: Kozacy, originally derived from Turkic Qazaqlar) are a traditional community of martial people living in the southern steppe regions of Eastern Europe and Asia. The Cossacks themselves make up a Cossack host, which allows to distinguish individual Cossack groups by their location, history, traditions and even military roles.

Although several theories exist on the formation of Cossacks, towards the end of the 14th century two Cossack hosts emerged — the Zaporozhian Host located in the lower Dnieper River and the Don Host located on the Don River. The Zaporozhian Sich joined by numerous serfs fleeing from Ukraine and other territories swelled into a powerful military force and led a rebellion against Polish domination in Ukraine. Under the leadership of a Cossack hetman Bohdan Khmelnytsky a Cossack Hetmanate was formed in 1649. Its prominence and the role of the Zaporozhian Cossacks began to diminish after the Treaty of Pereyaslavl with the Tsardom of Russia. The Cossack Hetmanate in Ukraine was abolished in 1764 and the Zaporozhian Sich was finally destroyed by the Russian army in 1775. Centuries later the Zaporozhian Cossacks would be viewed as progenitors of the modern Ukrainian nation.

The Don Cossack Host allied with the Tsardom of Russia since the 16th century began a systematic conquest of conquering and colonizing lands to secure her borders on the Volga, the whole of Siberia, the Yaik and the Terek Rivers, where newer Cossack hosts formed. By the end of the 18th century, the Cossacks were a special social estate (sosloviye) that served as border guards on national and internal ethnic borders as was in the case of the Caucasus War, would regularly supplied men to any conflict such as the numerous Russo-Turkish Wars. In return they enjoyed a vast social autonomy. This caused them to form a stereotypical portrayal of 19th century Russian Empire and its government abroad and domestically.

During the Russian Civil War Cossack regions became the main centres for the Anti-Bolshevik White movement, a portion of whom would form the White Emigre. At the hands of the Red Army and after its victory, the Cossack lands were subjected to famine, and suffered extensive repressions that were relaxed only in the mid-1930s. During the Second World War Cossacks fought for both the Soviet Union and collaborated with Nazi Germany. After the Collapse of the Soviet Union, Cossack lifestyle blossomed in Russia. Many fought in Post-Soviet Conflicts and there are special units in the Russian Military wholly made of them. Cossacks also have a parallel civil administration and police duties in their homelands and are now an integral part of the Russian society. There are also Cossack organizations in Kazakhstan, Ukraine and other countries.