Short answers, pulled from the story.
Ante Pavelić, a lawyer and politician from Zagreb, secretly contacted Benito Mussolini in 1927 to present his vision for an independent Greater Croatia. This meeting marked the beginning of a political movement that would eventually become known as the Ustaše.
Ustaše ministers Mile Budak and Milovan Žanić declared in May 1941 that the goal of new policy was ethnically pure Croatia involving killing one-third of Serbs, expelling another third, and forcibly converting the final third to Catholicism. State enacted race laws patterned after Third Reich which persecuted Jews, Romani, and Serbs collectively declared enemies of Croatian people.
On the 10th of April 1941 Slavko Kvaternik took control of police in Zagreb and proclaimed the formation of the Independent State of Croatia via radio broadcast. Ante Pavelić and several hundred Ustaše left their camps in Italy for Zagreb where he declared a new government on the 16th of April 1941.
Numbers of prisoners ranged from 300,000 to 700,000 in Jasenovac disputed figure. The complex built August 1941 through February 1942 contained three newer camps functioning until war's end including Ciglana, Kozara, and Stara Gradiška.
Blagoje Jovović Montenegrin shot Pavelić near Buenos Aires the 9th of April 1957. Pavelić died injuries after fleeing Argentina following his time hiding in Austria and Rome with help from Catholic clergy.