Uruguay's first constitution was adopted in 1830, following the conclusion of the three-year-long Cisplatine War in which Argentina and Uruguay acted as a regional federation: the United Provinces of Río de la Plata. Sponsored by the United Kingdom, the 1828 Treaty of Montevideo built the foundations for a Uruguayan state and constitution. Attempts to reform the 1952 constitution in 1966 led to the adoption of an entirely new document in 1967. A constitution proposed under a military dictatorship in 1980 was rejected.