Germany period.. West Germany was an artifact of WW II. and those four stable social democracies were also the national economies leading the way into industrialized economies and societies.
I distrust economic evaluations of societies because economists convert all social factors into money for the purpose of making things comparable. What is really important, though, is power. The difficulty in doing an analysis of power is that there is no reliable and consistent measure of power. It is invisible. But everyone knows who has it and who does not.
The twentieth century has been the century of war, and it was run in every case based on the draft. As Max Weber pointed out in Greece as long as wars were fought with chariots as the decisive weapon of war, bankers and aristocrats controlled society. When massed spearmen replaced chariots, they found the wars and then came home and demanded representation in government. This was Weber's analysis of the introduction of democracy into Greece.
The North Atlantic social democracies were all created during wars that were fought with massed armies filled by the draft. Power was removed in part from the plutocrats because they were no longer the essential element is the society during conflict. This started to fall apart as the Cold War ran down and it became clear that no one was going to fight another war in which the existence of the nation depended on the draft. It was, in fact, misused to create the Vietnam War, so Americans did away with it in the early 70's. This was at exactly the same time as the plutocrats (we call them conservatives in America) began taking control fo the national government. In essence, the plutocrats began to regain power in the 70's and without the need for the draft, there was no social force powerful enough to prevent them from doing that. So we got Reagan and the evangelicals. back in power.