Following the enactment of the McCarran Act, considerable uncertainty existed as to the type and the amount of state regulation necessary to render the federal antitrust laws inapplicable under the "to the extent that such business is not regulated by State law" provision. After several twists and turns in the immediately ensuing years, the state regulators, through the National Association of Insurance Commissioners and with the assistance and cooperation of the insurance industry, developed a series of model laws which ultimately were adopted by most states. The two major areas of concern were rating laws for property and liability insurance and unfair trade practice laws applicable to the entire insurance industry. As a result of this extensive activity at both the NAIC and the individual state levels, a nationwide system of insurance regulation became firmly implanted in all states to an even greater degree than ever before.

Although following the McCarran Act there continued to be tension and interaction between state insurance regulation and federal legislative and regulatory activity, at least until the early 1990s, the primacy of state insurance regulation remained intact despite some more recent erosion. Generally the states have regulated and the federal government (primarily Congress) has provided oversight.