During World War II Poland was the main scene of the Holocaust, the Porajmos, and the Nazi atrocities against the Polish nation. These genocides varied in how, when and where they were applied; Jews and Romani were targeted for immediate extermination and suffered the greatest casualties, while the Poles were targeted for destruction and enslavement within 15–20 years. Robert Gellately has called the Nazi racial policy of cultural eradication and mass extermination of people based on ethnicity a "serial genocide", since in its broader formulation it targeted multiple ethnic groups who the Nazis deemed "sub-human", including Ukrainians, Belorusians, Poles and Jews.