At the turn of the century, after the Industrial Revolution, the country was subject to new economic forces which required stricter regulation by the government.  As it became feasible and economically beneficial to form larger and larger companies, the ideal competitive capitalist market place became threatened.  The Sherman Act of 1890 sought to alleviate that threat by outlawing trusts: "Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is declared to be illegal." (Section 1)  This general restriction of trusts was interpreted in later case law.  At first it was applied broadly, outlawing any trust, but later was interpreted to restrict only trusts which were anti-competitive in nature.  The specific definition of anti-competitive is not given, but constantly worked out in case law as attitudes about competition change.

The Sherman Act, and the later Clayton Act (which sought to strengthen the Sherman Act) also make statements in reference to tying.  "Tying occurs when a seller conditions the sale of one product on the purchaser's agreement to buy a second (different) product. The tying product is the product the buyer wants and the tied product is the product the seller induces the buyer to purchase in order to obtain the tying product"  ( Antitrust Summary ).  Both the Sherman and Clayton Acts forbid tying.  The case of tying is most often disputed by challenging whether two products are tied, or whether they are one product.  This is pertinent to the Microsoft/DOJ case where Microsoft claims that Windows 95 and Internet Explorer are really one product.