IB raises an interesting, really a crucial point. I've read a bit of pre-history, going back about 10,000 years before the so-called Christian era, addressing the transition from nomadic and hunter-gatherer cultures to the new-fangled invention of agriculture.
I took my degree in Anthropology, so I do have some insight into this.
You are correct to a certain point.
Hunter-gatherers by necessity were small extended family groups, that over time expand to include other kin groups. The land determines how large a group can exist in one spot and how much range a group requires to sustain existence. Add in the aquatic borders and it often changes development into fisheries rather than agrarian society.
Hunter-gatherers are different from nomadic herding societies. Herders have a different range requirement, often larger in size depending upon the livestock and the eco-system.
Agro societies tend to grow to more stable and larger entities because the capability to feed larger groups from surpluses exist.
However, in all three types the same pressures exist. The Hunter-gatherer tends to remain small and loosely organized. It remains a relatively primitive society, regardless of the religious backing that grows up to regulate human intercourse.
Nomadic societies coalesce into larger groups and develop more complex governing activities, resulting in septs, clans, and tribes. Politically they form the first active ad-hoc governments, though it is mostly charismatic leadership that prevails bolstered by competence in specific fields of endeavor, such as the ability to get along and convenience others to follow ones decisions for animal husbandry, and migration, or combat, or hunting.
Fisheries are the next most complex but are limited to those areas where fishing is possible, seaside. Again these develop along the lines of nomadic herding societies for the same reasons, the primary activities require the men to be absent from the family for extended periods of time.
Agro societies are tied to smaller areas of land. Because growing crops allows a surplus of food for a relatively small effort from a small area, the families tend to group permanently in a single group. The group is concerned primarily with water access, protection of the land and family. This means that while the pressures upon the society are similar to the other types they are concentrated and more complex governmental systems are required to keep the peace and ensure uninterrupted supply of food for unrelated, or tenuously related groups using the same general area and resources.
Since the groups cannot easily separate if there is a feud as a hunter-gather or nomadic herder group can, they must have formal, regularized laws and entities to enforce those laws. Since the distribution of water is important, and since larger groups mean storage, defense and regulation and distribution of resources is paramount.
It's not a matter of greed, as it is of fair distribution of wealth. The hunter-gather has no wealth that isn't obtained by the efforts of all. The nomad has a more structured distribution of labor, but rewards individuals for contributions that enhance the survival of the primary groups.
Agro societies can afford to support non-contributing members, the old, the infirm, the incompetent. The richer the nomad society the more they can do this as well. However because agro societies can build upon regular expected results, charismatic leadership is less important, and the tolerance for non-contributors is enhanced to high levels. Because agro wealth is not as easily transportable it is subject to raiding and theft from others.
Enter organized war. The nomads and agro societies are opposed to each other in competition for land resources, and material wealth. The mobility of the nomads is offset by fortifications and an established trained and permanently standing military of the agro society.
While the nomads may have a great captain arise to gather the tribes together, they fall apart upon his death.
Not so with agro societies. They develop a regular succession of leadership to ensure the continuation of laws and governance that is vital to the group survival. Enter the divine right of kings. Religion is the proto-governemental form. What better way to enforce rules and regulations than by a deity who is controlling the environment and who must be appeased in order to ensure good weather and good crops.
Once the God-king connection is made, then nations arise from the city states.
This is the simple version.