If you are interested in why some countries are more populous than others, you should check population density, not the absolute number of people living there.

Let's look at these statistics:

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Country	Territory (km2)	Population (persons)	Population density (persons/km2)
Sweden	450,295	10,412,805	23
Finland	338,424	5,527,405	16.33
Norway	323,808	5,367,580	16,58
Denmark	43,098	5,814,461	134.91
Iceland	102,775	366,130	3.56

If you compare these five countries, you see big differences in both the size of the territory and of the population. Strictly speaking, Denmark is the most populous with appr. 135 persons living in each km2. The total population is of course smaller than that of Sweden (5.8 vs 10.4 million people), but the territory of Sweden is more than 10 times bigger!

From that, a couple of other questions can follow, e.g.

• Why does Sweden have the biggest territory?
• Why does Sweden have a bigger population density than Finland, Norway, and Iceland?
• Why is Denmark much more populous than the other four countries?
• Why is Iceland much less populous than the other four countries?
• How did the current population densities develop historically?

All of these are questions on there own.

Well Sweden has had many population booms and at first it had around the same as Denmark and Norway. Things like neutrality and area has also much to do with it. Iceland is an atlantic island that is small and not that populated until better housing development. Finland got independence in 1917 from Russian rule who where not that kind with human development of better housing and stuff like that