How many South Vietnamese were executed in killings ?
Since 1975 , Southern Vietnamese use the term " Bắc 54 " ( " Tonkin 54 " ) to refer to Northern Vietnamese who migrated to the South in 1954 ( as part of Operation Passage to Freedom , who were mainly political and religious refugees fleeing impending communist rule ) , and " Bắc 75 " ( " Tonkin 75 " ) to refer to Northerners who migrated to the South in 1975 onwards , many under this economic program .