Following the victory in WWI Serbs subsequently formed the Kingdom of Serbs, Croats and Slovenes with other South Slavic peoples. The country was later renamed the Kingdom of Yugoslavia, and was led from 1921 to 1934 by King Alexander I of the Serbian Karađorđević dynasty. During World War II, Yugoslavia was invaded by the Axis powers in April 1941. The country was subsequently divided into many pieces, with Serbia being directly occupied by the Germans. Serbs in the Independent State of Croatia (NDH) were targeted for extermination as part of genocide by the Croatian ultra-nationalist, fascist Ustaše. The Ustaše view of national and racial identity, as well as the theory of Serbs as an inferior race, was under the influence of Croatian nationalists and intellectuals from the end of the 19th and the beginning of the 20th century. Jasenovac camp was notorious for the barbaric practices which occurred in it. Sisak and Jastrebarsko concentration camp were specially formed for children. Serbs in the NDH suffered among the highest casualty rates in Europe during the World War II, while the NDH was one of the most lethal regimes in the 20th century. Diana Budisavljević, a humanitarian of Austrian descent, carried out rescue operations from Ustaše camps and saved more than 15,000 children, mostly Serbs.