Viking history traditionally begins in northern Europe with the first Scandinavian raid on England, in AD 793, and ends with the death of Harald Hardrada in 1066, in a failed attempt to attain the English throne. During those 250 years, the political and religious structure of northern Europe was changed irrevocably. Some of that change can be directly attributed to the actions of the Vikings, and/or the response to Viking imperialism, and some of it cannot.
Viking Age Beginnings
Beginning in the 8th century AD, the Vikings began expanding out of Scandinavia, first as raids and then as imperialistic settlements into a wide swath of places from Russia to the North American continent.
The reasons for the Viking expansion outside of Scandinavia are debated among scholars. Reasons suggested include population pressure, political pressure, and personal enrichment. The Vikings could never have begun raiding or indeed settling beyond Scandinavia if they had not developed highly effective boat building and navigation skills; skills that were in evidence by the 4th century AD. At the time of the expansion, the Scandinavian countries were each experiencing a centralization of power, with fierce competition.
Fifty years after the first raids on the monastery at Lindisfarne, England, the Scandinavians ominously shifted their tactics: they began to spend the winters at various locations. In Ireland, the ships themselves became part of the over-wintering, when the Norse built an earthen bank on the landward side of their docked ships. These types of sites, called longphorts, are found prominently on the Irish coasts and inland rivers.
The Viking economic pattern was a combination of pastoralism, long-distance trade, and piracy. The type of pastoralism used by the Vikings was called landnám, and although it was a successful strategy in the Faroe Islands, it failed miserably in Greenland and Ireland, where the thin soils and climate change led to desperate circumstances.
The Viking trade system, supplemented by piracy, on the other hand, was extremely successful. While conducting raids on various peoples throughout Europe and western Asia, the Vikings obtained untold amounts of silver ingots, personal items, and other booty, and buried them in hoards.
Legitimate trade in items such as cod, coins, ceramics, glass, walrus ivory, polar bear skins and, of course, slaves were conducted by the Vikings as early as the mid 9th century, in what must have been uneasy relationships between the Abbasid dynasty in Persia, and Charlemagne's empire in Europe.
Westward with the Viking Age
The Vikings arrived in Iceland in 873, and in Greenland in 985. In both cases, the importation of the landnam style of pastoralism led to dismal failure. In addition to a sharp decline in sea temperature, which led to deeper winters, the Norse found themselves in direct competition with the people they called the Skraelings, who we now understand are the ancestors of the Inuits of North America.
Forays westward from Greenland were undertaken in the very last years of the tenth century AD, and Leif Erickson finally made landfall on the Canadian shores in 1000 AD, at a site called L'anse Aux Meadows. The settlement there was doomed to failure, however.