Which treaty founded Mercosur in 1991?

The Treaty of Asunción founded Mercosur in 1991.

Argentina, Brazil, Paraguay and Uruguay signed the treaty in Asunción, Paraguay, on 26 March 1991. It set the process for creating a common market among the participating South American countries and established the name Mercado Común del Sur, commonly shortened to Mercosur.

The treaty called for the gradual elimination of tariffs and other barriers among the founding members, a common external tariff and coordination of economic policies. The arrangement was later supplemented by the 1994 Protocol of Ouro Preto, which gave Mercosur its institutional structure.

The Treaty of Asunción is sometimes confused with the Treaty of Montevideo. The 1980 Treaty of Montevideo established the Latin American Integration Association, while the 1960 Treaty of Montevideo created the earlier Latin American Free Trade Association. Mercosur’s founding document is specifically the Treaty of Asunción.