continued to grow, and the pirates looked further and further beyond the borders of the Baltic, and eventually into all of Europe. Historian Anders Winroth has challenged the "overpopulation" thesis, arguing that scholars are "simply repeating an ancient cliché that has no basis in fact." Economic model The economic model states that the Viking Age was the result of growing urbanism and trade throughout mainland Europe. As the Islamic world grew, so did its trade routes, and the wealth which moved along them was pushed further and further north. In Western Europe, proto-urban centres such as the -wich towns of Anglo-Saxon England began to boom during the prosperous era known as the "Long Eighth Century". The Scandinavians, like many other Europeans, were drawn to these wealthier "urban" centres, which soon became frequent targets of Viking raids. The connection of the Scandinavians to larger and richer trade networks lured the Vikings into Western Europe, and soon the rest of Europe and parts of the Middle East. In England, hoards of Viking silver, such as the Cuerdale Hoard and the Vale of York Hoard, offer good insight to this phenomenon. Critics of this model argue that the earliest recorded Viking raids were in Western Norway and northern Britain, which were not highly economically integrated areas. Alternative versions of the economic model point to economic incentives that stemmed from youth bulges, as young men were driven to maritime activity due to limited economic alternatives. Ideological model This era coincided with the Medieval Warm Period (800–1300) and stopped with the start of the Little Ice Age (about 1250–1850). The start of the Viking Age, with the sack of Lindisfarne, also coincided with Charlemagne's Saxon Wars, or Christian wars with pagans in Saxony. Bruno Dumézil theorises that the Viking attacks may have been in response to the spread of Christianity among pagan peoples. Because of the penetration of Christianity in Scandinavia, serious conflict divided Norway for almost a century. Political model The first of two main components to the political model is the external "Pull" factor, which suggests that the weak political bodies of Britain and Western Europe made for an attractive target for Viking raiders. The reasons for these weaknesses vary, but generally can be simplified into decentralized polities, or religious sites. As a result, Viking raiders found it easy to sack and then retreat from these areas which were thus frequently raided. The