D (Political concerns may lead a group of nations to form a cartel, a group of firms or nations that agrees to act as a monopoly and not compete with each other, to generate a competitive advantage in world markets. The Organization of Petroleum Exporting Countries (OPEC), the most famous cartel, was founded in the 1960's to increase the price of petroleum throughout the world and to maintain high prices in order to enhance the economies of its member nations.)