In February 1971, Colorado Party dissident senators Zelmar Michelini (who was later assassinated in 1976) and Hugo Batalla formed the left-of-center Broad Front coalition in a bid to break the historical two-party system of Colorados and Blancos. The Socialist Party of Uruguay (Partido Socialista del Uruguay-ÍÍÍÍ-PSU), one of Uruguay's oldest left-wing parties (founded in 1910 by Emilio Frugoni), was one of its principal members.

Another core Broad Front member, founded in 1921, was the Communist Party of Uruguay (Partido Comunista del Uruguay--PCU). Rodney Arismendi, PCU general secretary since 1955, returned to Uruguay in November 1984 after many years as a resident of Moscow he died in 1988 and was replaced by Jaime Pérez, a former union leader. One of Sanguinetti's first acts after taking office was to lift the restrictions on the PCU (which had been banned) and its Moscow-line newspaper El Popular. The PCU had only an estimated 7,500 members in early 1990, but its apparatus controlled the majority of the country's labor unions.

The Broad Front had a strong following in Montevideo, with a presence in all social classes and all generations. Under military rule (1973-85), the alliance's leader, General (Retired) Líber Seregni Mosquera, was arrested, the Broad Front was outlawed, and its activists were persecuted. When national elections were held in 1984, the military banned Seregni from running. Nevertheless, with Juan José Crottogini as its candidate, the Broad Front received slightly more than 21 percent of the total vote, compared with 18.5 percent in the 1971 national elections.

The Broad Front coalition generally agreed with the Sanguinetti government's foreign policy and political leadership stances, but it was fundamentally opposed to its economic policies. For example, the Broad Front favored increasing real incomes and opposed the government's export-oriented policy.

Internal power struggles between moderate and radical sectors weakened the Broad Front in the late 1980s. By late 1987, the Christian Democratic Party (Partido Demócrata Cristiano--PDC) and the People's Government Party (Partido por el Gobierno del Pueblo--PGP) were feuding with other coalition members over their demand that the alliance be redefined to give their own positions greater weight. The PDC and PGP wanted to reduce the hegemony of the Marxist groups and their undue influence on Seregni's public stances. In 1988 a PDC faction broke away and sought an understanding with one of the factions of the National Party. The PDC and PGP then proposed that the alliance should field two presidential candidates in the November 1989 elections: Seregni and PGP leader Batalla. The Broad Front's radical Marxist and communist sector, however, opposed the idea of running two candidates because they regarded the front as a party and not a coalition. In December 1988, therefore, the leftist parties of the alliance decided that Seregni would be the Broad Front's sole candidate but the PGP backed Batalla. The PDC and PGP withdrew from the alliance in February and March 1989, respectively, over the issue ec5of presisidential candidacies and the leftist control ofÍÍÍÍ the organization. Batalla's PGP, which accounted for about 40 percent of the alliance's electoral votes in 1984, had been responsible for eleven of the Broad Front's twenty-one representatives and three of its six senators.

By May 1989, the Broad Front consisted of fourteen parties. Smaller ones included the People's Victory Party (Partido por la Victoria del Pueblo--PVP) and the Uruguayan Revolutionary Movement of Independents (Movimiento de Independientes Revolucionario Oriental--MRO), a pro-Cuban group founded in 1961. Five parties were accepted as members in May 1989: the National Liberation Movement-Tupamaros (Movimiento de Liberación NacionalTupamaros --MLN-T) the 26th of March Movement (Movimiento 26 de Marzo--26 M) the Trotskyite Socialist Workers' Party (Partido Socialista de los Trabajadores--PST) the Grito de Asencio Integration Movement (Movimiento de Integración Grito de Asencio) and a faction of the PDC.

The MLN-T--a former urban guerrilla organization established in 1962 and disbanded by the armed forces in 1972--was given amnesty by the General Assembly in March 1985. The MLN-T reorganized and appeared in the political arena in July 1986 but was not legally recognized until May 1989. With several hundred members, it was politically insignificant. In order to run candidates in the November 1989 elections, the MLN-T, together with other ultra-leftist forces--the PVP, PST, and MRO---created the People's Participation Movement (Movimiento de Participación Popular--MPP).

In 1989 the Broad Front also included a subcoalition called the Advanced Democracy Party (Partido de Democracia Avanzada), which served as a front for the PCU the People's Broad Front Movement (Movimiento Popular Frenteamplista--MPF) the Broad Front Unity Faction (Corriente de Unidad Frenteamplista--CUFO) the Pregón Movement (Movimiento Pregón) Alba Roballo's left-wing Liberal Party (Partido Liberal), a sub-lema that joined in April 1989 the Nationalist Action Movement (Movimiento de Acción Nacionalista--MAN), a nationalist organization the Popular and Progressive Blanco Movement (Movimiento Popular Blanco y Progresista--MBPP), a moderate left-wing party and the Movement for the People's Government (Movimiento por el Gobierno del Pueblo--MGP), which became, in August 1986, the tenth political party of Uruguay to be created. The MGP subsequently merged with the PGP and adopted a social democratic program.

The Broad Front was organized like a communist party. It had a party congress with decision-making powers, under which was a central committee-like body called the national plenum. A president, Seregni, headed the 108-member national plenum, which met at least once every two months. A political bureau, which included the president, exercised day-to-day authority.

Data as of December 1990