Why did the Democratic Party and United Peasant Party support Poland’s first postcommunist government?

The Democratic Party (SD) and the United Peasant Party (ZSL) supported Poland’s first postcommunist government because they broke their long-standing alliance with the Polish United Workers’ Party (PUWP) following the political and economic crises of 1989.1

Previously, the SD and ZSL had existed only as subservient allies of the communist PUWP. However, after the Solidarity trade union achieved a sweeping victory in the partly free elections of June 1989, these parties shifted their allegiance. By joining forces with Solidarity, they enabled the formation of a coalition government led by Tadeusz Mazowiecki, the first noncommunist premier in eastern Europe since the late 1940s.123