Nothing puny about Scandinavia in those days. The Viking expansion was amazing. It was probably fueled by a population explosion in their homeland resulting from the Medieval Warm Period. Norsemen conquered and settled most of Britain, a large part of France, and Sicily, and founded the first Russian state. Much of the population of Britain, Ireland, and Russia has Norse blood, which may account for the daring and aggressive behavior of those nations in later centuries. Part of the problem with the Norse settlements in Greenland and Newfoundland is that they tried to live like Europeans (keeping cattle for example) as the climate drastically cooled as the Little Ice Age approached.
Most of the population of Scandinavia also has Norse blood, yet since 1720 those nations have been largely peaceful and at times even supine.