Very important historical source on the Guarani War. This is the Italian version of the letter from one of the Guarani Indians' leaders, sent to the Governor of Rio della Plata, José de Andonaegui, just at the beginning of the conflict. The letter was written in Guaraní: this Italian translation is certainly made by a Jesuit.
The Guarani War (1753–1756) was a series of armed engagements between a joint Spanish-Portuguese force and a group of Guarani Indians who actively resisted Spanish cession of their lands to the Portuguese. In 1750 a treaty was signed in Madrid that transferred the Portuguese settlement of Colonia to Spain in exchange for a several-hundred-mile wedge of Spanish territory east of the Uruguay River. Within this territory, however, were several Guarani missions under the control of the Society of Jesus (Jesuits). Discussions regarding its legality and wisdom took place both in the Spanish court and the Americas. The Jesuits sent missives to the Spanish king, first asking him not to sign the treaty and then criticizing him for ignoring their plea. Natives residing in the missions also protested against the order of evacuation.
Herzog: “In a famous letter dated 1753 and written in Guaraní, Nicolás Ñenguirú, leader of one of the Guaraní communities, asked the governor of Buenos Aires if the news was accurate. He suggested that outrageous as they were, the instructions must be the result of a Portuguese plot, not the genuine mandate of the Spanish king. After all, Spanish monarchs knew better. They had always thanked the Guaraní for their loyalty and service, and always promised them not only rewards but also protection. Under these circumstances, how could a Spanish king order an evacuation, which surely would cause the Guarani great harm, expelling them from their lands in order to give them to the Portuguese? How could the king mandate that they give away all that they had achieved by their labor? If such were the case, what was the point of bringing them to the mission in the first place? In his letter, Ñenguirú described the growing rage in his community and confessed that he could no longer control his men, who refused to listen to his explanations. But he himself was not clear of what he could say as he too did not understand how this could have happened.”
Nicolàs Ñeenguirú, corregidor of the town of Concepciòn, later become the leader of the uprising, in the final phase, when the Guarani were defeated and massacred in the great battle at Caaybaté, on 10 February 1756. The Indians found themselves surrounded, and although Nicolás attempted to negotiate terms, the Indians ended up fighting hand-to-hand.
See: Guaranis and Jesuits. Bordering the Spanish and the Portuguese Empires By Tamar Herzog; David Marley, Wars of the Americas: A Chronology of Armed Conflict in the Western Hemisphere, 1492 to the Present, Volume 2, 2008, p. 413.