Why New Orleans? The answer is tragically simple. Slaves, when they were brought over from Africa, were brought in large quantities to Louisiana and many #Caribbean islands, where the then largest plantations were. They were kept in massive groups, and many families, language groups, and even those taken from the same villages were able to still keep and maintain their African cultures and traditions, and pass them down for generations. The slaves primarily brought over in massive quantities at that time to Louisiana were primarily from West Africa.
While the rites were carried over from West Africa, the language morphed into French Creole. Louisiana voodoo venerates ancestors and instills great respect for elders.
Marie Laveau and her daughter, Marie Laveau II probably became the best known voodoo priestesses of the 19th century.
Born of a white plantation owner and his black mistress, Marie LaVeau was a free woman of color. She had access to many different parts of New Orleans society, and developed a huge following. Her St. John's rituals on the shores of Lake Ponchartrain drew thousands, showing her status as voodoo queen.
And what of gris gris?
Amulets, charms, whatever you want to compare them to. A staple of NOLA voodoo.