 Complete the following phrase:  Stalin was determined to punish those peoples he saw as collaborating with Germany during the war and to deal with the problem of nationalism, which would tend to pull the Soviet Union apart. Millions of Poles, Latvians, Georgians, Ukrainians and other ethnic minorities were deported to Gulags in Siberia. Previously, following the 1939 annexation of eastern Poland, thousands of Polish Army officers, including reservists, had been executed in the spring of 1940, in what came to be known as the 