Among the many worrying outcomes of the recent German elections was the further collapse of the main center-left party, the Social Democrats, which received only 20.5 percent of the vote, its worst performance since World War II.

Across Europe, social democratic or center-left parties are in decline. In elections this year in France and the Netherlands, the socialist and labor parties did so poorly that many question their future existence. Even in Scandinavia, considered the world’s social democratic stronghold, long-dominant parties have been reduced to vote shares in the high 20s and low 30s.

Even if you don’t support the left, this should be cause for concern. Social democratic parties were crucial to rebuilding democracy in Western Europe after 1945. They remain essential to democracy on the Continent today.

During the postwar years, social democratic parties acknowledged capitalism’s upsides and downsides. In contrast to Communists, center-left parties recognized that markets were the most effective engine for producing economic growth and prosperity. But in contrast to classical liberals and many conservatives, social democrats did not embrace markets wholeheartedly. Instead, the center-left insisted that it was possible — indeed, necessary — for governments to cushion markets’ most destabilizing effects. Capitalism would be kept subservient to the goals of social stability and solidarity, rather than the other way around.