Which international agreement created the Mercosur common market in South America?

The Treaty of Asunción created the Mercosur common market framework in South America.

Signed in 1991, the treaty committed Argentina, Brazil, Paraguay and Uruguay to a process of economic integration. Its objectives included free movement of goods and services, elimination of customs duties among members, a common external tariff and coordination of macroeconomic and sectoral policies.

The treaty did not instantly produce a fully functioning common market. It established a transition process, and later agreements supplied more detailed institutions and procedures. The 1994 Ouro Preto Protocol is especially important because it gave Mercosur legal personality and defined its decision-making structure.

Mercosur is therefore associated with both a founding treaty and later institutional instruments. The Treaty of Asunción is the canonical answer when asking which agreement launched the bloc.