Ustaše — Croatian ultranationalist movement and wartime regime

After the end of the First World War with the collapse of the Austro-Hungarian Monarchy, its southern states united to form the Kingdom of Serbs, Croats and Slovenes, later the Kingdom of Yugoslavia. The Ustasha movement was formed from groups that had formed the right-wing fringe of the Croatian opposition to the centralist and Serbian-hegemonic state order of the Kingdom in the 1920s.

The most important of these was the Hrvatska stranka prava, which had emerged from the right-wing, strictly anti-Yugoslav wing of the older party of the same name. Among the leading members of this party at that time was the later Ustasha leader and jurist AntePavelić. However, this and similar groupings were initially unable to gain greater influence. The dominant political force in Croatia at that time was and remained the Croatian Peasant Party led by Stjepan Radić.

At the end of October 1928, Ante Pavelić founded the initially illegal Ustasha. He was able to rely on anti-Yugoslav, revanchist and irredentist forces in Italy, Hungary and Bulgaria, as well as on legitimist circles in Austria and the revanchist movement in Germany. During a state crisis that followed the assassination of Croatian democrat Stjepan Radić in Belgrade by Puniša Račić, King Alexander I staged a coup d'état on 6 January 1929. He dissolved the parliament, suspended the 1921 constitution, and proclaimed a royal dictatorship that also banned the previous national symbols. A day later Pavelić emigrated to Italy, where he gathered emigrants from the Ustasha movement around him and formed them into a terrorist organization. In centres and camps in Hungary, Italy and Austria, the followers were trained for terrorist and subversive actions. In the asylum Pavelić wrote a program of the Ustasha, the "Statutes" (1932) and the "Principles", expanded in 1941.

The Ustasha saw itself as a Croatian independence movement against Serbian hegemony in Yugoslavia and for the development of a Greater Croatia including Bosnia, Herzegovina and Syrmia. The Serbian population was to be swiftly eliminated. The Ustasha developed into a fascist movement inspired by Mussolini and Hitler. From 1929 to 1934, it was actively supported by Mussolini's fascist regime in order to destabilize the state of Yugoslavia, which stood in the way of Italian domination of the Adriatic and the Balkans.

Although their followers were not very numerous in Yugoslavia, they infiltrated the Croatian Peasant Party and made intensive efforts to expand its right-wing and separatist forces. Some of their secret bases in the country were Catholic convents and seminaries. The government responded to the activities of the Ustasha by violently suppressing any potential resistance. In the process, several opposition figures not involved in the terrorist activities, including Milan Šufflay, were also murdered by agents of the Yugoslav secret service, prompting international protests.