Cajuns as a group and ethnicity came from the Acadia region of what is now Canada. The Brits fought a war with France and got Canada. The Acadians wanted to keep their land and resisted British encroachment. Eventually the Brits got fed up with this and expelled them all to other British colonies or France.
Many of the ones who went back to France were convinced by a guy called Henri Peyroux de la Coudreniere to resettle in Louisiana. Once there they comprised the largest ethnic group in that part of Louisiana. They carried on Acadian traditions and started new ones unique to Louisiana. This culture is called “Cajun.” The name itself is a phonetic transliteration of “Acadian” the way the Cajuns themselves pronounced it. Eventually the ‘A’ was dropped.
The Cajuns did not care for New Orleans, and still don’t. They were farmers and fishers and foresters, not bourgeois city-dwellers. Their city, the heart and center of Cajun people, is Lafayette.
Naturally, since they were next door neighbors, New Orleans culture and Cajun culture mixed, most notably the cuisines. Louisiana Creoles centered on New Orleans and the surrounding parishes. Their culture was way more cosmopolitan and had a lot of Spanish and Caribbean influence. A lot of dishes you think of as Cajun, have both Cajun and Creole versions, and you’ve probably never had the Cajun version, because Cajuns don’t leave home very often. I think of us as modern-day Hobbits.