Why are the economies of those countries in northern Europe with no population still good?

Northern Europe was very poor at the beginning of last century, and they were all small uncivilized agricultural countries.

In Sweden, for example, people are in dire straits. In the 1920s and 1930s, ordinary people immigrated to the American continent on a large scale, and the southern province of Scana almost ran away. Nearly one third of the country's population emigrated. There are many literary works that show the history of blood and tears of new immigrants. If the hometown is rich, who will emigrate?

Modern northern Europe mainly benefits from industrialization and informatization, with small population, small country and rapid economic transformation, and is the beneficiary in the process of globalization. Especially in the 1970s, the so-called gamlagodatiden was the last romance, and Ericsson, Nokia and Volvo all rose during this period.