Why does the text mention the Maya?

We are accustomed to thinking of military success as determined by quality of weaponry, rather than by food supply. But a
clear example of how improvements in food supply may decisively increase military success comes from the history of Maori New
Zealand. The Maori are the Polynesian people who were the first to settle New Zealand. Traditionally, they fought frequent fierce
wars against each other, but only against closely neighboring tribes. Those wars were limited by the modest productivity of their
agriculture, whose staple crop was sweet potatoes. It was not possible to grow enough sweet potatoes to feed an army in the field
for a long time or on distant marches. When Europeans arrived in New Zealand, they brought potatoes, which beginning around
1815 considerably increased Maori crop yields. Maori could now 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 yet acquired potatoes and guns. Thus, the
potato's productivity relieved previous limitations on Maori warfare, similar to the limitations that low-productivity corn agriculture
imposed on Maya warfare.

(Diamond, J. (2006). Collapse. London: Penguin.)