Marx stages of history

[NormalG]

Can someone explain to me how conditions in ancient slave society/ feudal society weren't not dire enough, or how they simply weren't fit, to set the stage for revolution into a society based on collective ownership of production?
How do we know for sure that capitalism will catapult us to this stage, and not just be transformed into another phase of majority in-subordinated by a small ruling group?

[Blake's Baby]

1 - socialism is not just the equalisation of poverty; it needs material production to back it up for the fulfillment of human needs. Previous modes of production couldn't do this; if everything had been collectivised in England in 1400 and given over to the workers and peasants, what would have happened is that all the workers and peasants would have become ever so slightly richer. But they would still have been two meals from starvation. Also of course, they would immediately have been invaded and probably conquered by France, ending the English Peasant Republic within a matter of months. It's not that conditions weren't bad, it's that the exploited classes weren't the classes that bore the new means of production. The new organisation of society that was emerging in Antique Slavery was what would become feudalism, administered by a military aristocracy. The new organisation of society that was developing in feudalism was capitalism, administered by a capitalist bourgeoisie. In both these cases, the 'revolutionary class' is not the same as the exploited productive class (firstly, the slaves, secondly the serfs).

2 - because the proletariat is both an exploited producer class, and the bearer of the new economic relations (socialism) there doesn't seem to be a place for an intermediate revolutionary class to take power. If the petite-bourgeoisie takes power, there's no reason for them to dismatle capitalism, they'll just run it with a different division of the spoils. So in reality what will happen is that they'll assimilate themselves to capitalism and become part of the bourgeoisie. Nothing will change, so it won't really be a 'revolution', just a coup; just different thieves around the table, dividing the stolen cake differently. If there is a political upheaval that results in a new order that still relies on wage labour and commodity production, then that's capitalism, whatever the new rulers claim.