Battle of Mbororé The Battle of Mbororé was a battle between the Guaraní living in the Jesuit Missions and the bandeirantes , explorers and adventurers based in São Paulo . It occurred on 11 March 1641 near the Mbororé mountain , now the town of Panambí in the Misiones Province , Argentina . Historic Antecedents . Need for Slaves and the beginning of the ' bandeiras ' . In the early 17th century , the Dutch landed on the Brazil coasts intending to settle there . They did this by using piracy to control navigation along the Atlantic coast , disrupting the Brazilian slave trade . This was a heavy blow to the Portuguese Empire , which needed slave labor to cultivate sugar and raise livestock , the industries which prevailed on the Atlantic coast of Brazil . As a result of this disruption , the Portuguese plantation owners began to make inroads into the local Indian population to make up the shortfall in slave labor . Moreover , due to the small quantities of silver , gold and precious stones found in the region of Piratininga , the scouts began to move towards the unknown interior of Brazil . These exploration and slave hunting groups , called bandeiras , were organized and managed as a business for the leading sectors of São Paulo , and their ranks included Mamluks ( Portuguese / Indian Mestizos ) , indigenous Tupi and Dutch who came to Brazil to try their luck . They had the support of Spanish and Paraguayan officials . In their advance toward the west , the frontiersmen never crossed the threshold specified by the Treaty of Tordesillas . Indirectly , the Bandeirantes of São Paulo became the vanguard of the Portuguese territorial expansion , which was consolidated by recovering Portugal ' s independence from Spain . First Attacks on the Jesuit Missions . By decree in 1608 , the governor of Asuncion , Paraguay , Hernando Arias de Saavedra ordered the Jesuits to areas surrounding the Parana River , Guayrá and areas inhabited by guaycurúes to found towns and evangelize the natives who inhabited these regions . Later , he included the peoples of Itatin ( north of Asuncion ) and Tape ( the current state of Rio Grande do Sul , Brazil ) . The Jesuits had begun this evangelization when the frontiersmen began arriving in eastern Guayrá . At first , they respected the indigenous peoples so treated by the Jesuits . However , the Guarani , concentrated in towns and skilled in various trades , represented a highly skilled workforce , defenseless because they could not bear arms as a result of another of the governor ' s decrees . Beginning in 1620 , bandeiras ' raids became increasingly aggressive , forcing the abandonment or relocation of some villages . Between 1628 and 1631 the bandeirantes ' leaders , Raposo Tavares and Manuel Antonio Pires Preto and their men periodically struck Guayrá , capturing thousands of Guarani who were then auctioned off at São Paulo . It is estimated that in the years 1628 - 1629 , raids captured some 5 , 000 Indians , of which only 1 , 200 reached São Paulo . The vast majority of them died in transit as a result of the slave traders ' treatment . By the year 1632 , 12 , 000 Guarani had been forcibly moved south , leaving the Guayrá region virtually deserted , in addition to population reductions in the nearby regions of San Ignacio Mini and Loreto in the territory of the present Province of Misiones . The Bandeirantes continued westward , striking Itatin in 1632 . Then followed the Tape , invaded during the years 1636 , 1637 and 1638 by successive bandeiras Raposo Tavares led by André Fernandes and Fernando Dias Pais . The Jesuits ' Defence . Montoya ' s Mission to the Crown . In 1638 , priests Antonio Ruiz de Montoya and Francisco Diaz Tano traveled to Spain in order to report to the King Felipe IV recent events in the missions . They wanted the King to lift his restrictions on the use of firearms by the natives . The recommendations of Ruiz de Montoya were accepted by the King and Council of the Indies , and dispatched several royal charters to Paraguay . By Royal Decree of 12 May 1640 , the Guaraní were allowed to take firearms for their defense , but if so directed by the prior Viceroy of Peru . The priests returned to Lima , with the intent of providing weapons to the natives , while Father Tano went to Rome to inform the Pope of the slave - hunting missions in order to obtain a papal protection . The Apostles of Caazapaguazú skirmish . Meanwhile , prior to the imminent danger of the frontiersmen crossing the Uruguay River , the regional priest Diego de Boroa , with the consent of the Governor of Asuncion and Real audience of Charcas , decided that the mission troops should receive firearms and begin military training . From Buenos Aires was sent eleven Spanish to organize the defense forces . In late 1638 , Father Diego de Alfaro crossed the Uruguay River with a number of Guaraní , armed and trained , with the intention of recovering indigenous territory and eventually face the bandeirantes who roamed the region . After some sporadic encounters with the forces of São Paulo , the troops were joined by Father Alfaro and 1 , 500 Guarani led by Father Romero . He then formed an army of 4 , 000 missionaries who advanced to the ravaged reduction Apostles Caazapaguazú where bandeirantes were entrenched after several partial defeats . The armed clash was the first decisive victory of the Guarani Paulistas , who abruptly fled after surrendering . São Paulo ' s government prepares the counterattack . Torn apart , the Bandeirantes forces returned to São Paulo to tell authorities what happened . Coincidentally , at that same time , Father Tano came to Rio de Janeiro from Madrid and Rome . He had in his possession royal charters and Papal Bulls condemning the bandeiras ' conducting human trafficking with the indigenous people . Both events produced a backlash in the government of São Paulo which , in agreement with the plantations , expelled the Jesuits from the city . The city organized a huge bandeira with 450 Dutch and Portuguese armed with rifles and muskets , 700 canoes and 2 , 700 Tupi archers , led by Manuel Pires . The aim of the expedition was to take and destroy everything that was in Uruguay and Paraná rivers , taking all potential slaves .