One of the first acts of the Administration of the future Marquês de Pombal was to put into execution the Treaty of 1750, which was the keystone of the peninsular policy of D. João V. To assure and consolidate the good relations with Spain, that had begun with the exchange of princesses at Caia, was his principal desire. To liquidate the old disagreement about the Colónia do Sacramento, which had cost both the Portuguese and Spaniards quantities of blood since its foundation on the Rio Plata by D. Manuel Lobo, was the end and purpose of this treaty.
The monarch hoped, by marrying the Princess D. Maria Bárbara with the Prince of Asturias, the future King of Spain, and his elder son D. José with D. Mariana Vitória, to liquidate the old question by means of this “treaty, that had been concluded through the efforts of Alexandre de Gusmão”. In spite of everything, and notwithstanding the language and the “tone of this memorable treaty”, and the sincerity and good intentions of the two Crowns, the treaty produced “discontent, as much in Spain as in Portugal”.