The United Kingdom of the Rio de la Plata and Peru is a sovereign state in South America. Also known as Rio de la Plata, or River Plate for the Commonwealth. It borders Brazil to the west; Patagonian Republic to the south; and New Granada to the north. Rio de la Plata is a constitutional monarchy. The king is the Head of State and of the judiciary, armed forces and the main executive functions. The parliament is the legislature. And the viceroy is the Head of the Government, the secondary executive powers, the diplomatic powers and the mediator between the king, the parliament and the people.