It has to do with the farmland. Denmark is flat and lacks mountains, which makes for good farmland. Sweden has some good farmland in the south, but in the North it has more mountains and cold weather. Norway has some usable farmland, but it is few and far between, as Norway is hilly, mountainous and cold. When you have more farmland, you can sustain a higher population on less land, which means that the country will have a higher population density than a country with less productive farmland. So, because of this, Denmark naturally has a higher population density than Norway and some parts of Sweden.
| Country | Agricultural Output (Crops and Animals) in mil EUR |
|---|---|
| Denmark | 10450 |
| Sweden | 5720,29 |
| Norway | 5036,67 |
| Country | Agricultural Output (mil EUR per km^2 ) |
|---|---|
| Denmark | 0,243 |
| Sweden | 0,014 |
| Norway | 0,016 |
Source: Eurostat (2013 Data)
I hope the 2013 data does not break the 20 year rule. The data is less than 20 years old, but is just meant to illustrate the historic farmland in Scandinavia, which modern data can give a approximation.
The underlying data if some are interested in it:
| Country | Agricultural Output (Crops) in mil EUR |
|---|---|
| Denmark | 3682,63 |
| Sweden | 2783,91 |
| Norway | 1659,75 |
| Country | Agricultural Output (Animals) in mil EUR |
|---|---|
| Denmark | 6767,37 |
| Sweden | 2936,38 |
| Norway | 3376,92 |
| Country | Population density (Persons per km^2 ) |
|---|---|
| Denmark | 130,8 |
| Sweden | 23,6 |
| Norway | 16,7 |
| Country | Population |
|---|---|
| Denmark | 5602628 |
| Sweden | 9555893 |
| Norway | 5051275 |
Source: Eurostat (2013 Data)
When was this true? Sweden has roughly 4 million more people currently.