A little more background on New Orleans, before and after the Civil War...
I don't believe there is anywhere on the continent that has seen more governmental change. The land was once controlled by Native Americans, then the French, Spanish, French, Americans, Confederates, and then Americans again. As some locals have joked, they could have worn out a flagpole changing national flags. Maybe that's why they tend to be less focused on national politics and more inwardly focused, looking back at their history and realizing that national affiliation isn't always a permanent thing; therefore, their primary loyalty should be to New Orleans. It's a unique mindset that we don't see much anywhere else.
It was founded where it is for somewhat questionable reasons. Natchez came first. Without any historical weather data, it was the southernmost point along the Mississippi that was obviously flood-proof, and too far inland to be highly vulnerable to coastal storms. With lower ground on the other side of the river, a flood of any size would surely go in the direction away from the town. Then they got a little bolder and tried Baton Rouge, the southernmost reasonably high ground along the river. And then they went quite possibly (still open to debate) a step too far, founding New Orleans on a sliver of river bottom mud barely above sea level. The Indians must have thought the French had lost their minds.
To this day, the culture is very much like what you would expect from a city that knows it's not supposed to be there, and feels to its core that every day could be its last. Let the good times roll. Party while you still can, because anything could happen tomorrow. It could all be gone in a matter of hours, so celebrate every minute that life gives you; every song, every drink, every moment of sunshine, every kind word.
Under French and Spanish rule, there was no religious freedom, no separation of church and state. Saint Louis Cathedral was essentially the territorial capitol building. Louisiana was ruled by the man who officiated over mass on Sunday morning at that altar. The massive, lower buildings on both sides were administrative offices where the church managed the details of running the colony. Citizens who failed to conform to Catholic teachings were publicly punished out front, in what we now call Jackson Square. Slaves were also auctioned and sometimes punished there. It was a harsh time.
Spain controlled the city for a few years, as a result of a peace treaty having to do with a war in Europe that didn't otherwise touch this area. But the Spanish only wanted New Orleans to prevent the French from having it, so that it couldn't be used as a naval base for the French to harass Spanish ships sailing to and from Texas, Mexico, and various islands to the south. In other words, they didn't love New Orleans. That's why the people didn't stick around when it reverted to French control, after another peace treaty. Today, there's no lasting Spanish cultural influence remaining in in New Orleans, except for the architecture.
Why architecture? Because there was a massive fire that destroyed most of the French Quarter while it was under Spanish ownership, and the Spanish rebuilt it. New Orleans has been destroyed by storms, floods, warfare, and fire, but it was the fire that came last, so the Spanish did the most recent French Quarter rebuilding. Those fancy townhouse railings and awning supports have been duplicated and sold nationwide as French designs, but they are actually Spanish. Only a few French homes have survived, small and ordinary dwellings that nobody notices when they walk by. And of course, Saint Louis Cathedral.
The French brought with them many customs from their home country, including Mardi Gras and above ground burial. Some tourist carriage drivers will tell you that bodies buried below ground will float out during floods, but I've taken photos that prove otherwise. Yes, there are conventional cemeteries there, and the coffins stay put. Above ground burial, not so much. Rent must be paid to the owners by subsequent generations, or they will evict your bones. No, I'm not kidding. Those cemetery owners are not nice people. No survivors left to pay? Out you go.
French settlers, out of town mostly, began to intermarry with Cajuns, Acadia Indians from eastern Canada exiled there by the British for being too friendly with the French in Quebec. This was the start of Creole culture. (I use Creole with a capital C to refer to that culture which is specific to Louisiana, as opposed to creole with a small c for French mixed race ethnic groups scattered all over the world.) Then free blacks got involved in it, many from Caribbean islands. This was (and is) a truly nonracial culture. Most Creoles today have a mix of French, Indian, and African blood. Creole purists don't care about your race, as long as you were born in Louisiana, you're a member of the Catholic Church, and you speak French at home as your first language.
Back in the city, slaves enjoying Sunday afternoons off in Congo Square on the edge of the French Quarter combined musical ideas from their homes in Africa and European ideas that they had heard more recently, and invented jazz. It's one of the few examples in world history where we know exactly when and where a major, significant style of music was created.
English speaking whites have been moving into New Orleans since Thomas Jefferson acquired the land for the US, slowly eroding the Creole culture, pushing it out of town to the west, toward Lafayette. 70 years ago, the French Quarter had two daily French language newspapers. In my visits there, I've only overheard two conversations conducted in French. Now I understand why Quebec fights so hard for their language and culture, which can be so easily lost through bilingualism, in one generation.
At this point in time, there are many residents of New Orleans who hope to make the city more American, more typical and ordinary, more Southern. I hope they fail, or move away. We have all the rest of America to be typical America. We only have one New Orleans. So, visit it, love it, hate it, do whatever you want to do, as long as you don't move there and try to change it.
When you honor, respect, and celebrate New Orleans Mardi Gras, you are honoring, respecting, and celebrating all of this rich heritage, the legacy of the most exotic city in America.