started sailing and raiding due to a need to seek out women from foreign lands was expressed in the 11th century by historian Dudo of Saint-Quentin in his semi-imaginary History of The Normans. As observed by Adam of Bremen, rich and powerful Viking men tended to have many wives and concubines; and these polygynous relationships may have led to a shortage of women available to the Viking male. Consequently, the average Viking man may have felt compelled to seek wealth and power to have the means to acquire suitable women. Several centuries after Dudo's observations, scholars revived this idea, and over time it became a cliché among scholars of the Viking Age. Viking men would often buy or capture women and make them into their wives or concubines; such polygynous marriages increase male-male competition in society because they create a pool of unmarried men who are willing to engage in risky status-elevating and sex seeking behaviors. The Annals of Ulster states that in 821 the Vikings plundered an Irish village and "carried off a great number of women into captivity". One common theory posits that Charlemagne "used force and terror to Christianise all pagans", leading to baptism, conversion or execution, and as a result, Vikings and other pagans resisted and wanted revenge. Professor Rudolf Simek states that "it is not a coincidence if the early Viking activity occurred during the reign of Charlemagne". The ascendance of Christianity in Scandinavia led to serious conflict, dividing Norway for almost a century. However, this time period did not commence until the 10th century, Norway was never subject to aggression by Charlemagne and the period of strife was due to successive Norwegian kings embracing Christianity after encountering it overseas. Another explanation is that the Vikings exploited a moment of weakness in the surrounding regions. Contrary to Simek's assertion, Viking raids occurred sporadically long before the reign of Charlemagne; but exploded in frequency and size after his death, when his empire fragmented into multiple much weaker entities. England suffered from internal divisions and was relatively easy prey given the proximity of many towns to the sea or to navigable rivers. Lack of organised naval opposition throughout western Europe allowed Viking ships to travel freely, raiding or trading as opportunity permitted. The decline in the profitability of old trade routes could also have played a role. Trade between western Europe and the rest of Eurasia suffered