For over a hundred years people have described the tendency of a capitalist enterprise to concentrate wealth and power. There is no fine distinction between small diverse competitive capitalism and oligopoly, they are different stages of the life cycle.
This is because small diverse enterprises proliferate at first in the growth stage and then winners start to emerge. When a crisis hits, the larger players snap up the bankrupt smaller players at bargain prices and get their best employees too. Over a series of crises, the market consolidates into oligopoly. Once the national market is nearly consumed, the remaining players look abroad to expand markets. There is nothing controversial about this, it is taught in business school.
https://hbr.org/2002/12/the-consolidation-curve
This of course assumes a life cycle that starts domestically. Many ventures instead start abroad witnessing an opportunity to exploit cheap labor, lax regulations, or a unique natural resource. The western governments then assist the western companies in securing the opportunity, usually through gangster tactics. The resources are then extracted from the country, processed by the company into higher value goods, and resold to the originating country.