The Repatriation of Cossacks after WW2, also known as the Betrayal of the Cossacks, the Tragedy of Drau or the Massacre of Cossacks at Lienz refers to the forced repatriation

Repatriation

Repatriation is the process of returning a person back to one's place of origin or citizenship. This includes the process of returning refugees or soldiers to their place of origin following a war...

 to the USSR of the Cossacks and ethnic Russians

Russians

The Russian people are an East Slavic ethnic group native to Russia, speaking the Russian language and primarily living in Russia and neighboring countries....

 who were allies of Nazi Germany

Nazi Germany

Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

 during the Second World War.

The repatriations were agreed to in the Yalta Conference

Yalta Conference

The Yalta Conference, sometimes called the Crimea Conference and codenamed the Argonaut Conference, held February 4–11, 1945, was the wartime meeting of the heads of government of the United States, the United Kingdom, and the Soviet Union, represented by President Franklin D...

; most of the repatriated people were Soviet citizens, although some claimed to have left Russia before the end of the Russian Civil War

Russian Civil War

The Russian Civil War was a multi-party war that occurred within the former Russian Empire after the Russian provisional government collapsed to the Soviets, under the domination of the Bolshevik party. Soviet forces first assumed power in Petrograd The Russian Civil War (1917–1923) was a...

, or to have been born abroad.