Capital concentration, of course, does not mean that in a given market, dominance will continue forever by the same firms, no matter what. However, the fact that the companies that dominate a market can change over time is no great cause for joy (no matter what supporters of free market capitalism claim). This is because when market dominance changes between companies all it means is that old Big Business is replaced by new Big Business:
"Once oligopoly emerges in an industry, one should not assume that sustained competitive advantage will be maintained forever. . . once achieved in any given product market, oligopoly creates barriers to entry that can be overcome only by the development of even more powerful forms of business organisation that can plan and co-ordinate even more complex specialised divisions of labour." [William Lazonick, Business Organisation and the Myth of the Market Economy, p. 173]
Hardly a great improvement as changing the company hardly changes the impact of capital concentration or Big Business on the economy. While the faces may change, the system itself remains the same.
In a developed market, with a high degree of monopoly (i.e. high market concentration and capital costs that create barriers to entry into it), new companies can usually only enter under four conditions:
2) They get state aid to protect them against foreign competition (e.g. the South East Asian "Tiger" economies or the 19th century US economy) - "Historically, political strategies to develop national economies have provided critical protection and support to overcome. . . barriers to entry." [William Lazonick, Op. Cit., p. 87]
3) Demand exceeds supply, resulting in a profit level which tempts other big companies into the market or gives smaller firms already there excess profits, allowing them to expand. Demand still plays a limiting role in even the most oligopolistic market (but this process hardly decreases barriers to entry/mobility or oligopolistic tendencies in the long run).
4) The dominant companies raise their prices too high or become complacent and make mistakes, so allowing other big firms to undermine their position in a market (and, sometimes, allow smaller companies to expand and do the same). For example, many large US oligopolies in the 1970s came under pressure from Japanese oligopolies because of this. However, as noted in section C.4.2, these declining oligopolies can see their market control last for decades and the resulting market will still be dominated by oligopolies (as big firms are generally replaced by similar sized, or bigger, ones).
Usually some or all of these processes are at work at once.
Let's consider the US steel industry as an example. The 1980's saw the rise of the so-called "mini-mills" with lower capital costs. The mini-mills, a new industry segment, developed only after the US steel industry had gone into decline due to Japanese competition. The creation of Nippon Steel, matching the size of US steel companies, was a key factor in the rise of the Japanese steel industry, which invested heavily in modern technology to increase steel output by 2,216% in 30 years (5.3 million tons in 1950 to 122.8 million by 1980). By the mid 1980's, the mini-mills and imports each had a quarter of the US market, with many previously steel-based companies diversifying into new markets.
Only by investing $9 billion to increase technological competitiveness, cutting workers wages to increase labour productivity, getting relief from stringent pollution control laws and (very importantly) the US government restricting imports to a quarter of the total home market could the US steel industry survive. The fall in the value of the dollar also helped by making imports more expensive. In addition, US steel firms became increasingly linked with their Japanese "rivals," resulting in increased centralisation (and so concentration) of capital.
Therefore, only because competition from foreign capital created space in a previously dominated market, driving established capital out, combined with state intervention to protect and aid home producers, was a new segment of the industry able to get a foothold in the local market. With many established companies closing down and moving to other markets, and once the value of the dollar fell which forced import prices up and state intervention reduced foreign competition, the mini-mills were in an excellent position to increase US market share.
This period in the US steel industry was marked by increased "co-operation" between US and Japanese companies, with larger companies the outcome. This meant, in the case of the mini-mills, that the cycle of capital formation and concentration would start again, with bigger companies driving out the smaller ones through competition.
So, while the actual companies involved may change over time, the economy as a whole will always be marked by Big Business due to the nature of capitalism. That's the way capitalism works -- profits for the few at the expense of the many.