The principle was established by Paul v. Virginia. In that 19th-century U.S. Supreme Court case, the Court held that issuing an insurance policy was not a transaction of commerce within the meaning of the Commerce Clause. That decision supported the historic state-based regulation of insurance. This changed in 1944 when United States v. South-Eastern Underwriters Association held that insurance transactions conducted across state lines could constitute interstate commerce subject to federal regulation. Congress then responded with the McCarran-Ferguson Act, which restored and preserved the primacy of state regulation unless federal law specifically provides otherwise. Therefore, option C is the correct answer for the original “insurance is not commerce” principle. Option D is the opposite result because South-Eastern Underwriters treated interstate insurance business as commerce. Option A is important but not the original case establishing the non-commerce principle. Reference topics: Paul v. Virginia, South-Eastern Underwriters, McCarran-Ferguson Act, State Regulation of Insurance.