On 6 April 1941, Axis forces invaded Yugoslavia. Poorly equipped and poorly trained, the Royal Yugoslav Army was quickly defeated. The country was then dismembered and the extreme Croat nationalist and fascist Ante Pavelić, who had been in exile in Benito Mussolini's Italy, was appointed Poglavnik (leader) of an Ustaše-led Croatian state – the Independent State of Croatia (often called the NDH, from the Croatian: Nezavisna Država Hrvatska). The NDH combined almost all of modern-day Croatia, all of modern-day Bosnia and Herzegovina and parts of modern-day Serbia into an "Italian-German quasi-protectorate". NDH authorities, led by the Ustaše militia, subsequently implemented genocidal policies against the Serb, Jewish and Romani population living within the borders of the new state. Ethnic Serbs were persecuted the most because Pavelić and the Ustaše considered them "potential turncoats" in what they wanted to be an ethnically pure state composed solely of Croats. Racist and antisemitic laws were passed, and ethnic Serbs, representing about thirty percent of the NDH's population of 6.3 million, became targets of large-scale massacres perpetrated by the Ustaše. By the middle of 1941, these killings reached degrees of brutality that shocked even some Germans. The Cyrillic script was subsequently banned by Croatian authorities, Orthodox Christian church schools were closed, and Serbs were ordered to wear identifying armbands. Mile Budak, the Croatian Minister of Education, is reported to have said that one-third of Serbs in the NDH were to be killed, one-third were to be expelled, and one-third were to be converted to Roman Catholicism. The Ustaše then established numerous concentration camps where thousands of Serbs were mistreated, starved, and murdered.
Glina is a small market town in the Banovina region of Croatia located about 55 kilometers (34 miles) south of Zagreb. In 1931, the town itself had a population of 2,315 people and was inhabited mostly by Serbs, Croats, and Jews. Shortly after the Ustaše took power, the Croatian Minister of Justice,
Mirko Puk, established a base in the town.