In the United States, the principal law regulating anticompetitive activity is the 
Sherman Antitrust Act of 1890.The American courts have interpreted this as applying only to conduct between 
two or more parties and only to contracts that unreasonably restrain trade.Section 1 of the act prohibits contracts, agreements, and conspiracies that restrain 
interstate or international trade.In determining whether a particular activity violates ?1, the courts ordinarily do so 
on a case-by-case basis using a so-called rule of reason.???