On the Effects of Improvements in Food Supply

"When Europeans arrived in New Zealand, they brought potatoes, which beginning around 1815 considerably increased Maori crop yields. Maori couldnow grow enough food to supply armies in the field for many weeks. the result was a 15-year period in Maori history, from 1818 until 1833, when Maori tribes that had acquired potatoes and guns from the English sent armies out on raids to attack tribes hundreds of miles away that had not acquired potatoes and guns. Thus, the potato's productivity relived previous limitations on Maori warfare, similar to the limitations that low-productivity corn agriculture imposed on Maya warfare."

'Collapse: How Societies choose to fail or succeed' Jared Diamond

A very telling statement.