Among other things, he was born in Bosnia and was raised around Muslims.

He later morphed his formative experiences with a weird racial ideology which posited that Muslims and Catholics in Bosnia are all Croat people, and also je rejected democracy as political method after failures in politics.

Basically, Croatia itself was always far more culturally diverse compared to his native lands outside of Croatia, so he concluded that his fervently nationalist idea of merging Bosnia and Croatia into a single state would never get enough votes anyway.

So he went abroad, started a terrorist group. The group was tolerated by Italy, who then installed him to run an Italian puppet state, under the condition that he gives up any claims over Dalmatia which they wanted for themselves, and also to fuck off away from the coastline as far as possible.

(Dalmatia had been its own thing for about a century until WW1 within Austria-Hungary, and about 400 years prior to that it was part of the Venetian Republic.)

So, unelected, with no actual or factual claim to legitimacy; and running a state that was entirely under the Italian crown, and not even in charge of the military administration (which was split into German and Italian areas of control), Pavelic limited himself to the only things je could.

One of these was genocide i.e. ethnic cleansing, because in the Ustase opinion if you eradicate Serbs then winning elections for a party like his might become possible some day.

Another thing was reconstructing “Croatian” identity around Bosnia and especially Herzegovina, which is where all the key Ustasha leaders came from (rather than from Croatia proper) and which were really post-Ottoman lands, with an entirely different history and relationship to ethnicity compared to Habsburg Croatia, the reconquered Slavonia, or the formerly Venetian Dalmatia.

Another thing, which his modern-day Croatian nationalist fans choose to ignore, was the attempt to islamicize Croats. He plopped a giant mosque in Zagreb city center, which never had a mosque before, and built tall minarets next to it, so that WW2 residents of Zagreb could hear Islamic calls to prayer every day.

(At the same time, and only maybe 1 km away, they gradually demolished the old Jewish synagogue, and even made a public exhibition with photographs of its gradual deconstruction.)

Pavelic was not really “Croatian” in the sense that his ideas or solutions were shaped by living in actual Croatia. Rather, he was an immigrant from Bosnia who never really found a way to fit into the age-old multi-cultural fabric of the capital city.

So he basically brought the Balkans to Croatia, and in a way set off to colonize Croatia proper.

And as a narrative designed to emphasize this message, the Ustashe talked a lot about 10th century King Tomislav (a guy from 1.000 years ago who briefly ruled this territory), which itself was lore promoted in royal Yugoslavia around 1925, the anniversary of the alleged historic event, the crowning of Tomislav.

(Vichy France had a similar story, in an attempt to explain how a government that only controls half of France is 100% patriotic, they heavily promoted stories of Vercingetorix, the Gauls and the Romans.)

They also imposed a very particular and made up archaic form of “Croatian” identity, introduced weird puritan language rules, and interpreted all the pan-Slavic movements and ideas that came before them as either wholly “Croatian” in nature, or outright unacceptable.

It’s ironic because these days we are seeing a surge in far-right narratives which pitch Pavelic and his ilk as sort of freedom fighters for an independent Croatia.

In reality, his “country” was not independent, neither formally nor factually. Parts of it were freely given away to neighboring powers. And even the national identity promoted by him literally would not be recognizable or acceptable to his fans today.

The ethnic cleansing was just part of it, although probably “terrorism” would be a better term for it - Ustasha were legitimately and unapologetically a terrorist organisation ever since their foundation.

Their cruelty was well documented (by them) and the purpose was to use that propaganda and terror to make undesirables move away on their own volition.

But he was not the first guy to have had those ideas, in fact ethnic cleansings and genocides have been a feature of all post-Ottoman societies after the Ottoman Empire ceased to exist. And Pavelic himself was a product of exactly that environment.