Subcarpathian Ruthenia was a region in the easternmost part of Czechoslovakia which was annexed by Hungary in March 1939.
From 1939, laws were introduced banning Jews from attending school or from running businesses. In the summer of 1941, Hungarian authorities deported about 18,000 Jews from Subcarpathian Ruthenia. Those men who avoided deportation were conscripted into slave labour.
In April 1944, 17 main ghettos were set up in the region where 144,000 Jews were held until they were transferred to Auschwitz-Birkenau concentration and extermination camp in occupied Poland between May and June 1944. 90,000 of the more than 100,000 Jews from the region were murdered in the Holocaust.
The vast majority of the third and fourth groups of the Boys came from Subcarpathian Ruthenia.