The change that led to commodity production being generalized was the process of primitive accumulation. Primitive accumulation involved the forceful separation of producers from their land, and created a new social class defined by its freedom to sell its labor power (in the sense that it was not actually tied to the means of production, as in slavery) and its freedom from ownership of the means of production (as in its expropriation).

Prior to this point, commodity production did exist, but it did not define economic life in pre-capitalist epochs and was distinct from capitalist commodity production. Pre-capitalist commodity production generally manifested as the exchange of products of separate, independent producers who created and exchanged their own products. The difference, at the most basic level, between this simple commodity production and capitalist commodity production, is that the latter depends on labor power itself assuming the commodity form.

The fact that, under the capitalist mode of production, the working class possesses no means of production and has to sell its labor power for wages is what ensures that the creations of labor, across the board, become commodities. That is why Marx, in a footnote in Chapter Six of Capital Volume One, remarks that,

“The capitalist epoch is therefore characterised by this, that labour-power takes in the eyes of the labourer himself the form of a commodity which is his property; his labour consequently becomes wage-labour. On the other hand, it is only from this moment that the produce of labour universally becomes a commodity.”

Likewise, it’s incorrect to say that wage labor existed to any significant extent in pre-capitalist epochs. For Marx, it was the process of primitive accumulation that created the necessary conditions for generalized wage labor. In Chapter 26 of Capital Volume One, he states that,

“Hence, the historical movement which changes the producers into wage-workers, appears, on the one hand, as their emancipation from serfdom and from the fetters of the guilds, and this side alone exists for our bourgeois historians. But, on the other hand, these new freedmen became sellers of themselves only after they had been robbed of all their own means of production, and of all the guarantees of existence afforded by the old feudal arrangements.”

That is to say, the dominance of wage labor requires as a precondition the abolition of pre-capitalist modes of production.