Government policy for dealing with monopoly. Antitrust laws aim to stop abuses of market power by big companies and, sometimes, to prevent corporate mergers and acquisitions that would create or strengthen a monopolist. There have been big differences in antitrust policies both among countries and within the same country over time. This has reflected different ideas about what constitutes a monopoly and, where there is one, what sorts of behavior are abusive. In the United States, monopoly policy has been built on the Sherman Antitrust Act of 1890. This prohibited contracts or conspiracies to restrain trade or, in the words of a later act, to monopolize commerce. In the early 20th century this law was used to reduce the economic power wielded by so-called "robber barons", such as JP Morgan and John D. Rockefeller, who dominated much of American industry through huge trusts that controlled companies' voting shares. Du Pont chemicals, the railroad companies and Rockefeller's Standard Oil, among others, were broken up. In the 1970s the Sherman Act was turned (ultimately without success) against IBM, and in 1982 it secured the break-up of AT&T's nationwide telecoms monopoly. In the 1980s a more laissez-faire approach was adopted, underpinned by economic theories from the Chicago school. These theories said that the only justification for antitrust intervention should be that a lack of competition harmed consumers, and not that a firm had become, in some ill-defined sense, too big. Some monopolistic activities previously targeted by antitrust authorities, such as predatory pricing and exclusive marketing agreements, were much less harmful to consumers than had been thought in the past. They also criticized the traditional method of identifying a monopoly, which was based on looking at what percentage of a market was served by the biggest firm or firms, using a measure known as the Herfindahl-Hirschman index. Instead, they argued that even a market dominated by one firm need not be a matter of antitrust concern, provided it was a contestable market. In the 1990s American antitrust policy became somewhat more interventionist. A high-profile lawsuit was launched against Microsoft in 1998. The giant software company was found guilty of anti-competitive behavior, which was said to slow the pace of innovation. However, fears that the firm would be broken up, signaling a far more interventionalist American antitrust policy, proved misplaced. The firm was not severely punished. In the UK, antitrust policy was long judged according to what policymakers decided was in the public interest. At times this approach was comparatively permissive of mergers and acquisitions; at others it was less so. However, in the mid-1980s the UK followed the American lead in basing antitrust policy on whether changes in competition harmed consumers. Within the rest of the European Union several big countries pursued policies of building up national champions, allowing chosen firms to enjoy some monopoly power at home which could be used to make them more effective competitors abroad. However, during the 1990s the European Commission became increasingly active in antitrust policy, mostly seeking to promote competition within the EU. In 2000, the EU controversially blocked a merger between two American firms, GE and Honeywell; the deal had already been approved by America's antitrust regulators. The controversy highlighted an important issue. As globalization increases, the relevant market for judging whether market power exists or is being abused will increasingly cover far more territory than any one single economy. Indeed, there may be a need to establish a global antitrust watchdog, perhaps under the auspices of the world trade organization.