KNOJ was created based on a directive by Marshal of Yugoslavia, Josip Broz Tito, on 15 August 1944. As liberated territories expanded, the corps was established to allow Partisan military intelligence organization (Department for People's Protection, OZNA) continued focus on core tasks. The corps comprised about 80,000 men at its peak. The first commander was Jovan Vukotić (1907–1982) and the supervision lay with the political commissar Vlado Janić (1904–1991). KNOJ was rarely used at the front, instead fell under the direction and supervision of OZNA.
In July 1944, just before the formation of KNOJ, there were about 5,000 soldiers in defense units that dealt with security on liberated territories. At the end of the war, in May 1945, KNOJ consisted of eight divisions. The basic tasks of the KNOJ were to cleanse the liberated territory from all kinds of enemies, to help the National Liberation Committees in organizing life in the free territory and securing the borders of Yugoslavia. After the end of the war, KNOJ, in cooperation with other security forces, was the basic factor for the security of the country's borders and the destruction of remaining quisling units.
The National Defense Corps of Yugoslavia was disbanded in January 1953, and its jurisdiction was taken over by Yugoslav People's Army and Militsiya (police).
Crusaders in Croatia and Bosnia-Herzegovina were mostly former personnel of the Armed Forces of the NDH, mostly Ustaše, but also Croatian Home Guard, members of the former Croatian legionnaire divisions of the Wehrmacht and non-military Ustaše members.
Croatian historian Zdravko Dizdar describes the Crusaders mostly as soldiers and other individuals associated with the NDH army who went underground for fear of their lives, because the Partisans had engaged significant OZNA resources in tracking them down, which led to either their summary executions, judicial executions, or long prison sentences. Any known associates of eliminated Crusaders, mostly their relatives, were also often targeted by the Partisan military and political apparatus.
Soldiers who returned from abroad in mid-1945 acted in unorganized, small groups, which provided a foundation for future guerrilla forces.
Despite the name, the Crusaders were not a religious movement. Religion was a banner that they used to distinguish themselves from atheist communists. Most supporters of the Crusaders were Catholic but there were also many Muslim members, including the Crusader commander in Sarajevo, Hasan Biber. They also stated that the Yugoslav partisans were a Serbian anti-Croat movement. There was also support for the Crusaders in anti-Communist emigrant communities, especially in Spain, Argentina, Canada, the United States, and West Germany.
The Yugoslav Department of State Security (UDBA) blamed the Croatian Peasant Party (HSS, also called Mačekovci) and the Catholic clergy for the creation of the Crusaders. The UDBA claimed that the name "Crusaders" was coined in June 1945, when remaining elements of the Croatian Armed Forces and the clerical part of the HSS joined. The UDBA states that remains of Ustaše bandits under wing of a Pastoral Letter took the name "Crusaders". The Crusaders' insignia was the Croatian Coat of Arms with the white cross, or the Ustaše sign with the "U" replaced with a white cross. Their flag was the Croatian tricolor with the slogan "For Croatia and Christ Against Communists" ("Za Hrvatsku i Krista protiv komunista") on one side, and "By this sign you will Conquer" ("U ovom ćeš znaku pobijediti") on the other. The Croatian guerrillas were called various names: Crusaders (križari), Cavers (Špiljari), Škripari, Kamišari (cavers), Jamari (cavers), Šumnjaci (forest people), even White Partisans (bijeli partizani). The name "Crusaders" was used universally, while the other names were used regionally