The reason capitalists replaced aristocrats was because they had the capital or the power as it were. The aristocrats had grown complacent in their ways with the huge amount of land they owned used extremely inefficiently. You can see this in Britain where the land was being cultivated in very unoptimal ways that earnt very small amounts of money in comparison to new methods developed and implemented by the innovators of the time.
These innovators were very often the middle class and instead of having their power given by right of god and their blood, they had to earn it. Since they didnt have the space and vast amounts of capital the aristocrats had, they needed to innovate in order to make profits. This is where things such as the cotton mill came into play since it was a manpower multiplier i.e. 1 man with 1 spindle can make 1 bolt of cloth, 1 man with 1 machine-loom can make 10 bolts of cloth with much more consistent quality.
So over time as the families of the aristocrats grew larger and they needed to spread the same amount of money over a larger amount of people, their capital shrank. While the middle class that was actively seeking to earn money grew richer and began buying the land of the aristocrats perpetuating the cycle. Over time the money generated by using the old methods was so minimal that they in terms of power sort of faded out while the capitalists replaced them.
Keep in mind that is a very general statement since the aristocracy in Russia remained extremely powerful until the 1916 revolution while the French Revolution removed their aristocrats (but installed more capitalist ones instead). Britain kept its power but watered it down over time until all that the common man has left to remember is the names of things i.e. Sandwich, Perth, etc.
EDIT:
http://www.thelandmagazine.org.uk/articles/short-history-enclosure-britain - Textile exports exploded benefiting the industrialists that invested in it, American imported food undercut British exports reducing the profits of the aristocrats that relied on food exports to supplement their income.
http://www.wise.xmu.edu.cn/Master/News/NewsPic/200911992321411.pdf - England began to import more food than it produced