It is possible capitalism doesn't cause monopoly power, but this would require the most successful business to also have altruistic aims and to have both the profit motive and the desire to keep competition.

Are monopolies a feature of capitalism?

The defining characteristic of monopoly capitalism is that developed capitalist economies are seen as essentially dominated by firms which operate in oligopolistic industries.

Does unregulated capitalism lead to monopolies?

Over time, because the biggest economic winners are likely to keep winning and losers are likely to keep losing, unregulated capitalism inevitably leads to the monopolistic power of fewer and fewer winners and thus more and more losers, ultimately leading to all wealth residing in the hands of the few.