In the case of De Beers Consolidated Mines, Ltd. v. United States in 1944, the U.S Supreme Court ruled against De Beers Consolidated Mines and its associated companies for violating American antitrust laws. The court found that De Beers had created a global monopoly on diamond sales by controlling both supply and price through agreements with other international mining companies. This was deemed to be an illegal restraint of trade under the Sherman Antitrust Act because it prevented competition in the market place and artificially inflated prices for consumers. Despite arguments from De Beers that their operations were outside U.S jurisdiction as they were based primarily in South Africa, this defense was rejected by the court which held that any company doing business within America is subject to its laws regardless of where it is headquartered or incorporated.

In the dissenting opinion for De Beers Consolidated Mines, Ltd. v. United States (1944), it was argued that the Supreme Court should not have jurisdiction over this case as it involves a foreign corporation with no presence or assets in the U.S., and therefore cannot be subject to its antitrust laws. The dissent emphasized respect for international law and sovereignty of other nations, arguing that applying U.S. law to foreign entities operating entirely outside of American borders is an overreach of judicial power. It also pointed out potential diplomatic issues arising from such decisions, cautioning against imposing American legal standards on global commerce without clear congressional intent or international agreement.