MERCOSUR.   The historic rivals Argentina and Brazil first explored economic collaboration in the early 1980s. Both countries underwent political transitions in the early and mid-1980s from military to civilian regimes—Argentina in 1983 and Brazil in 1985. In November 1985 the newly elected democratic presidents—President Raúl Alfonsín of Argentina and President José Sarney of Brazil—met to inaugurate a new bridge at Iguaçú Falls. They agreed to create a binational commission to study the possibilities of increased economic cooperation and integration, and in 1986 the Programa de Integración y Cooperación Económica entre Argentina y Brasil (Program for Integration and Economic Cooperation between Argentina and Brazil, PICAB) was announced. Later in 1986 the two presidents signed the Act of Brazilian-Argentine Friendship in Brasília, and they announced that the two countries would pursue a policy of peaceful nuclear development...