Answer:
The North European Plain
Explanation:
The North European plain is the most populated region of the four mentioned in the question.
This was not always the case, and until the Middle Ages, the North European Plain was sparsely populated. However, ever since, its population has been growing, because despite having a climate that is wet and cool the majority of the year, the soil is very fertile, and the lack of physical geographical barriers makes it easier for human dwelling.
