The suffering of Slovenes in the Ustasha camps was closely related to the German occupation of Slovenia in 1941. On 18 April 1941 the SS leader, Heinrich Himmler, approved procedures that would lead to the eviction of foreign elements in Donja Štajerska (Lower Styria), according to which the deportation of 260,000 Slovenes was foreseen.
The government of the Independent State of Croatia reached an agreement with the Germans during a conference in Zagreb on 4 June 1941, according to which the Independent State of Croatia approved the Slovene deportation plan, agreeing that the Independent State of Croatia would deport as many Serbs to Serbia as the number of Slovenes to be deported to Croatia.
In the first deportation wave in July 1941, 349 priests were exiled to the Independent State of Croatia by the Nazis. They were taken care of by the Zagreb Archdiocese. They were housed in monasteries and parishes in Slavonska Požega, Đakovo and Zagorje.
The second wave began on 11 July 1941, during which 9,800 Slovenian citizens in 21 rail transports were exiled. All but one of the transports was housed in the assembly camp for refugees in Slavonska Požega. Later, the Ustashas relocated them to Bosnia and north-west parts of the Independent State of Croatia.
For Slovenes already living in Croatia, the foundation of the Independent State of Croatia only meant further assimilation and the undermining of their national and cultural identity. Companies owned by Slovenes had Croatian supervisors assigned to them and all Slovenes in Zagreb were obliged to register with the police between 18 and 23 August 1941.
The persecution of Slovenes in the Independent State of Croatia was not based on their nationality, but on the Decree on the transportation of undesirable and dangerous persons to forced internment in assembly and labour camps (from 25 November 1941). As opponents of the Ustasha regime, they were arrested and deported to Jasenovac, Stara Gradiška and Lepoglava camps.
According to the testimonies of surviving inmates, several hundred Slovenes were imprisoned in Camp III (Brickworks), of whom only a few survived.