Was Viking expansion driven by the ship or the society?

The short answer

• A scarcity of farmland at home. Norway's mountains, forests and rock left only about 3 percent of its land available for cultivation. Good farms along the fjords were limited and passed to eldest sons. Younger sons and landless men had reason to seek wealth elsewhere. Ships could take them abroad to trade or raid, and later carry families west to clear and defend land for farms.
• Silver from the Islamic world. Silver minted by the Abbasid caliphate and its neighbors traveled north in the ninth and tenth centuries, through Russian rivers and across the Baltic, in exchange for furs and enslaved people. Scandinavian finds include hundreds of thousands of these dirhams. Silver enriched towns such as Hedeby and enabled chieftains to reward followers; places where wealth accumulated could also attract raiders.
• Unguarded wealth across the North Sea. Coastal monasteries in Britain and Ireland held gold, silver and books, sometimes on islands chosen for solitude. They were exposed to crews arriving by sea. Political divisions offered other opportunities: Northumbria had civil wars, and the Frankish empire of Charlemagne's heirs split after 840. A ship gave its crew the mobility to strike a weak point and leave before an army could gather.
• A society organised for voyages. A voyage depended on ties established at home. Chieftains drew followers through gifts and oaths, farms supplied wool, and women did much of the spinning and weaving needed for sails. Crews also needed iron and timber, while assemblies helped settle disputes that might keep men at home. These resources and institutions made it possible to send people abroad in the hope of returning richer.

What it changed

Settlement follows the raiders west. Routes first used by raiders could also bring families looking for farms. Norse settlers took the Northern Isles, Hebrides and Faroe Islands in the ninth century. In the 870s they crossed about 500 kilometres of open sea to Iceland, a volcanic island without a king or native people. Chapter 3 follows the society they established, including enslaved people brought from Gaelic lands.

Norse towns and kingdoms in Britain and Ireland. Some raiders acquired territory and governed it. Dublin became a Norse trading town from 841; after 866 York became the capital of a Norse kingdom. In the 870s and 880s the Danelaw placed eastern England under Scandinavian law. Markets and churches in these centers connected the Norse world to western Europe and later colonies depended on those connections.

Walrus ivory enters the story. In the 890s Ohthere described a trade in walrus tusks and hide ropes from the far north to southern markets. Greenland's Norse later hunted walrus far up the west coast, and ivory became an economic engine for their colony. Chapter 4 follows the trade and the dependence that could grow around a single export.