How did the discovery of agriculture in the neolithic period change human political structures?

The Neolithic agriculture revolution made fundamental
changes in the organization of human societies. Compared to hunter-gatherer societies,
even fairly crude slash-and-burn agriculture is an extremely efficient method of
obtaining food. Agriculture intensifies food production for a given land area allowing
for substantial increases in population density. Agriculture also favours fixed
locations, as opposed to the necessary mobility of nomadic and hunter-gatherer means of
obtaining food. The combination of population density and fixed locales lead to
urbanisation and increasingly complex political structures. Irrigation, as developed in
Mesopotamia and Egypt, in particular, requires large scale and long term cooperation
among large groups of people.

Even more important, the
relative efficiency of agriculture food production results in an economic surplus, i.e.
no longer are all the people in the community engaged primarily in subsistence level
food gathering. This allows for some specialization of labour, and the development of
crafts -- e.g. potters who can trade pots for food -- leading to technological
innovation.