Contrary to popular American myth, the first real Thanksgiving celebrated on what was to become American soil was held on September 8, 1565. Pedro Menendez de Aviles and his Spanish landing party which included Father Francisco Lopez de Mendoza, celebrated a Mass of Thanksgiving in site of the native Americans of the Seloy tribe who occupied the area. It was the feast of the Nativity of the Blessed Virgin.
Afterwards, the Spanish and Native Americans shared a meal. Exactly what they ate was unclear, but the Spanish probably made a pork and garbonzo bean stew with garlic, since that is what they brought with them on their 5 ships. If the Seloy contributed to the meal, it could have included turkey, fish, venison, corn and tortoise.
So, the first Thanksgiving began with a Catholic Mass. How cool is that?
"Slavery ended in medieval Europe only because the church extended its sacraments to all slaves and then managed to impose a ban on the enslavement of Christians (and of Jews). Within the context of medieval Europe, that prohibition was effectively a rule of universal abolition. "— Rodney Stark