"Pirara dispute" (spanish "cuestión de Pirara", portuguese "questão do Pirara") is the name associated to a territorial dispute bewteen Brazil and Guyana, over a territory which extented on 33,200 km² of land between the brazilian state of Roraima and south-west Guyana.
After the arbitration of 1899 which declared the cession of the Guayana Esequiba (the easternmost part of Venezuela) to Guyana, then a colony of the british empire, Britain had to solve a new problem regarding the boundaries of the colony with Brazil.
During 1835 Robert Schomburgk, an explorer of german origin, was surveying the territory of Guyana under orders of the british government. He sent some information back to his country which explained how the portuguese didn't effectively control the region, and he suggested that the english should annex this territory to their colony.
The english court approved these news and decided to send a missionary, Thomas Yound. Yound reached the region of Pirara and converted some indigenous people to the protestant religion, teaching them to speak english and effectively making sure that the english could claim this territory as theirs.
The president of the Pará province, General Soares de Andréia ordered that the english missionary be moved away; Yound then was forced to go with some indios converted to the english religion.
In 1840 Robert Schomburgk created a map, which he sent to England, where the regions of Tacutu, Mau and part of Surumu were shown as proprieties of the indigenous tribes. With this map Schomburgk set a new frontier between the two countries, marking the Cotingo and Surumu rivers as boundaries.
The map attracted the attention of the public opinion in britain. The brazilian presence in the region was waning, because the royal family of Portugal had modernized the southern parts of the country but left the northern regions in decadence. In 1842 a brazilian ambassador went to London to suggest that the dispute should be solved with a neutral arbitrage.
The diplomatic dispute remained on hold until 1898, when Brazil accepted the proposal to hand the problem to a neutral party: the italian government was chosen. Lawyer Joaquim Nabuco defended the interests of Brazil at the court of Vittorio Emanuele III.
In 1904 a final decision was reached: the italian king declared that 19,630 km² should go to Great Britain (later Guyana when the colony gained its independence), and 13,570 km² should go to Brazil, finally establishing the boundaries of the countries in the region.
With this arbitration England obtained access to the Amazon river through the Ireng and Tacutu rivers.
at the Spanish Wikipedia