Competition law is a young subject which is still very much being created by the interactions of governments, consumers, judges, economists, academics, competition authorities and companies. Its real concern is the proper limits on the power of private companies. It takes as given the desirability of free markets as the best route to wealth, innovation and consumer welfare.
The problem faced in competition cases is when and how to control the behaviour of companies which undermine the functioning of free markets. Powerful companies can and do seek to exclude rivals so that they can reap monopoly profits. The job of competition law is to prevent this where it is the result of unfair or abusive behaviour. At the same time, we do not wish to remove incentives for companies to compete by criticising them when they do.
United States law goes back to early cases aimed at preventing abuse by John Rockefeller's Standard Oil case and comes up to date with the attempts to control Microsoft's behaviour. European competion law is more recent but has been a key part of the creation of a single market in Europe.