Antitrust law protects the public from companies that attain an undue domination of the marketplace via mergers, tying 1 product to another, vertical integration, and other practices tending to eliminate competition or bar entry into the market to newcomers.
In the early 1980s, Microsoft was a much smaller company than it is today. However, it had already established a reputation of being a predator, a greedy predator. They were known to terminate licenses mercilessly once they figured out a way to clone the given technology, regardless of whether it was legal or not. Back then, Microsoft had some enthusiastic competition. The biggest of which were Borland (programming), Ashton-Tate (databases), Visicalc and Lotus (spreadsheets), as well as Wordstar and WordPerfect (word processors). All of these companies have now either merged out of existence or are completely defunct, with the exceptions of Borland and Lotus (which are barely afloat). Microsoft now has the leading product in each sector of the market once occupied by these firms. The company was responsible for ridding itself of these early competitors by either buying them out or simply driving them into the ground. This early disregard set the tone for how Microsoft does business even today.
Microsoft's advantage comes from their domination of operating systems. "By definition, if the OS maker creates applications, they will run better with the OS than a third party's, and the OS owner can, over time, create modifications that will make this even more so,” (Rapacious 1). Microsoft has the power to leverage their dominance in operating systems to gain a large market share in the various application sectors. They have always been able to do this and as a result have been able to get, or achieve, whatever it is that they have wanted. This is the vertical integration that the antitrust laws talk about.
In a July 1994, settlement, the Justice Department came to an agreement with the software giant over the antitrust charges it had filed against the company.