A clearer light is perhaps thrown on the matter if we examine the political condition of the Scandinavian countries at this time. In Norway we find that the concentration of kingly authority in the hands of Harold Fairhair after the middle of the 9th century led many of the more independent spirits to leave Norway and adopt a Viking life in the West or to settle in new homes in Iceland. So strong was the spirit of independence that when Harold Fairhair received the submission of the Vikings of the West after the battle of Hafrsfjord, many of them rather than endure even a shadowy overlordship abandoned their Viking life and settled down to peaceful independence in Iceland. It is quite possible that earlier attempts at consolidation on the part of previous petty Norwegian kings may have had similar results. Of the condition of Sweden we know practically nothing but we have sufficient information about the course of events in Denmark at this time to see that it probably tended to hasten the development of the Viking movement. Throughout the first half of the 9th century there were repeated dynastic struggles accompanied probably by the exile, voluntary or forced, of many members of the rival factions. External causes also were certainly not without influence. From the 6th century down to the middle of the 8th, the Frisians were the great naval and trading power of North-West Europe. They had probably taken some part in the conquest of England and, during the 7th and 8th centuries, the whole of the coast of the Netherlands from the Scheldt to the Weser was in their hands. Their trade was extensive, their chief city being Duurstede a few miles south-east of Utrecht. The northward expansion of the Franks brought them into collision with the Frisians in the 7th century. The struggle was long and fierce but in the end the Frisians were defeated by Charles Martel in 734 and finally subjugated by Charlemagne in 785. The crushing of Frisian naval power and the crippling of their trade probably played no unimportant part in facilitating the Scandinavian advance, and it is curious to note that while there is considerable archaeological evidence for peaceful intercourse between the west coast of Norway and Frisian lands in the 8th century, that evidence seems to come to an end about the year 800, just when Frisian power finally declined. There can be no doubt also that the conquest of the Saxons by Charlemagne at the close of the 8th century, bringing Franks and Danes face to face along the Eider boundary, made the latter uneasy.