Capitalism developed over hundreds of years and is inextricable from European colonialism. The shift to capitalist relations themselves being ubiquitous is just a couple hundred years old, but the conquest by the bourgeoisie goes back more like 500-700 years.

The idea of a “free market” is an invention of capitalism in the last few hundred years. Laissez-faire was coined by French businessmen in the late 1600s.

Most of the Roman low and medium skill artisans were slaves, actually.

But capitalism is best recognized by the proliferation of commodities, as it is made up of various wage labor capitalist enterprises producing large quantities of fungible goods for market. A chair is a chair is a chair and you can buy 50 varieties of basically the same thing at the furniture store. Under capitalism, all economic life is governed by this: you work a wage labor job and you buy everything else (commodities made by other wage laborers).

Rome did not have such a system. A vastly larger proportion of goods were made at home by oneself or by servants or by slaves. When goods were purchased they would have mostly been produced by slaves or petty bourgeois artisans or apprentices. Wage laborers still existed, but they were not typical.

An important part of Marxist analysis is to focus on the shift from quantitative to qualitative in social development. The high proportion of wage laborers is something that typefies capitalism, but wage laborers have existed for a long time. At some point there was a watershed moment - or watershed many decades - where the material forces that increased this proportion crossed various thresholds to create a new ruling class that became dominant and started throwing their weight around (capitalists). The capitalist class was in no way dominant in Rome.

Capitalism is not about individuals being greedy. Calling capitalists greedy is like calling fish greedy for needing water. The capitalist system requires constant profit maximization to prevent firms from crumbling, the capitalists are tasked with ensuring this, generally by (at first) maximizing exchange value of their product and minimizing costs (usually labor), then later using monopoly position to charge economic rent. In the heart of empire, financialization has meant trying to skip the first step via large financial investment up front, like with tech monopolies. The system itself forces exploitation, dispossession, colonialism, and ultimately crisis and war.

Historical empires conquered for reasons we often don’t really know specifically, as the accounts we have are written by victors with limited access and understanding. But ancient peoples were just as sophisticated as us and subject to material forces as us, so it was certainly not just being greedy. The economic base can force hands, for example. The Roman slave and debt system was unsustainable and required debt jubilees and war and invasions to be maintained, for example. For the ruling class of Rome, was maintaining the empire only greed or was it what they were taught to do as the moral and right thing?

The mode of production is never human nature. Human nature is a factor, but the mode of production is something that is socially constructed and subject to material constraints, like tools and the environment in which people live.

But socializing and sharing empathy is virtually universal, and the impetus to share food or shelter or community is something that capitalist society teaches us to avoid. So one of the things we strive for through the abolition of capitalism is the restoration of human connections and care that are currently robbed from us. So I can totally see where you are coming from re: the extent to which the communism we want to build constitutes a return. But it is even more a step forward, a transformation into the future constructed from the bones of the present.

Re: what Marx called “primitive communism”, which we might better call egalitarian societies based on hunting and gathering and sometimes agriculture, such societies have actually existed everywhere people have lived. You can find clear historical examples of such societies in the Americas and Australia, yes, but also in the Middle East, Ukraine, Great Britain, Ethiopia, Pakistan/India, China, etc. As you mention, any of these societies did not have written records or they were lost, but we can understand how they lived based on their homes, food, tools, dress, cohabitation, and spatial distribution of all these things.