Treaty of Madrid
The Treaty of Madrid was significant because it substantially defined the modern boundaries of Brazil. However, the resistance of the Jesuits to surrendering their missions and the refusal of the Guarani to be forcibly relocated led to the nullification of the treaty by the subsequent Treaty of El Pardo, signed by both countries in 1761. The opposition by the Guarani led to the Guarani War of 1756. The terms of the Treaty of Madrid, with a few exceptions, were re-established in the First Treaty of San Ildefonso in 1777, and that treaty was again negated in 1801.