The plague

In case you wonder why so many deaths occur around 1710-1711, which in my family tree is especially visible among the Dutch inhabitants of the island of Amager (just South of Copenhagen), a part of the answer might be, that these people were closely connected to the sea (as well as farmers), and many ships from the Baltic area landed their cargos in Copenhagen and on the island of Amager. The plague in this area, and in the whole of Scandinavia, may well have entered through the most commonly used landing sites and harbours, as it was the case in the earlier plague pandemics, both in the Baltic area, Scandinavia, England, Italy and other countries. An estimated one-third of East Prussia’s population died in the plague of 1709–1711. The plague of 1710 killed two-thirds of the inhabitants of Helsinki. An outbreak of plague between 1710 and 1711 claimed a third of Stockholm’s population, as well as one third of Copenhagen’s population.

A specific plague epidemic that followed the Great Northern War (1700–1721, Sweden vs. Russia and allies) wiped out almost 1/3 of the population in the Baltic region.

The great famine
In Europe, the Medieval Warm Period ended sometime towards the end of the 13th century, bringing harsher winters and reduced harvests. In the years 1315 to 1317 a catastrophic famine, known as the Great Famine, struck much of North-West Europe. The famine came about as the result of a large population growth in the previous centuries, with the result that, in the early 14th century the population began to exceed the number that could be sustained by productive capacity of the land and farmers. This is also believed to have an impact on the large death toll that ocurred in the following plague pandemics.

Source: wikipedia