Dr Mark Collard, Professor of Archaeology at the University of Aberdeen and currently the Canada Research Chair at the Simon Fraser University in British Columbia, Canada, believes that changes in society had led to a desperate shortage of marriage partners.
The growth of polygamy and social inequality in the Late Iron Age meant that richer men took many wives, or concubines, causing an in-balance in the male-female sex ratio.
Suddenly young poor men had little chance of securing a wife unless they became rich and well-known quickly, says Prof Collard. And raiding was a shortcut to heroism and treasure, he believes.
“What is clear is that the sex ratio would have been substantially biased and increasing through time, and even small amounts of bias can have a big effect,” he said.
“In a population where just a few powerful older men are able to have multiple concubines you end up with a large number of young single men quite rapidly. Some men would have two to three wives, but the Norse sagas say that some princes had limitless numbers.
“So raiding was away to build up wealth and power. Men could gain a place in society, and the chance for wives if they took part in raids and proved their masculinity and came back wealthy.
“Because polygynous marriage increases male-male competition by creating a pool of unmarried men, it increases risky status-elevating behaviour.”
Thus monogamy leads to rather more peaceful societies.