power, and also characterized the October 1956 revolution as a "popular uprising", in the words of Pozsgay, whose reform movement had been gathering strength as Communist Party membership declined dramatically. Kádár's major political rivals then cooperated to move the country gradually to Western-style democracy. The Soviet Union reduced its involvement by signing an agreement in April 1989 to withdraw Soviet forces by June 1991. While Grósz favoured reforming and refining the system, the "democracy package" went well beyond the "model change" he advocated to change the system within the framework of Communism. However, by this time, Grósz had been rapidly eclipsed by a faction of radical reformers including Pozsgay, Miklós Németh (who succeeded Grósz as prime minister later in 1988), Foreign Minister Gyula Horn, and Rezső Nyers, the original architect of the New Economic Mechanism. This faction now favoured a "system change"–jettisoning Communism altogether in favour of a market economy. By the summer of 1989, it was clear that the MSZMP was no longer a Marxist-Leninist party. In June, a four-man executive presidency replaced the Politburo. Three of its four members–Nemeth, Pozsgay and Nyers–came from the radical reform faction, with Nyers becoming party president. Grósz retained his title of general secretary, but Nyers now outranked him–effectively making Nyers the leader of Hungary. National unity culminated in June 1989 as the country reburied Imre Nagy, his associates, and, symbolically, all other victims of the 1956 revolution. A national round table, comprising representatives of the new parties, some recreated old parties (such as the Smallholders and Social Democrats), and different social groups, met in the late summer of 1989 to discuss major changes to the Hungarian constitution in preparation for free elections and the transition to a fully free and democratic political system. In October 1989, the MSZMP convened what would be its last congress. The party voted to disband and re-establish itself as the Hungarian Socialist Party (Magyar Szocialista Párt, MSZP), a Western European-style social democratic party with Nyers as its first president. Unable to slow down, let alone stop, the momentum toward a full "system change," Grósz eventually led a faction of Communists out of the MSZP to form a revived Hungarian Socialist Workers' Party, now the Hungarian Workers' Party. The biggest changes by far came on 16–20 October 1989. In a historic session, Parliament adopted a package of nearly 100 constitutional amendments that almost completely rewrote the 1949 constitution.