The third part of the economic order formed after the Second World War was the General Agreement on Tariffs and Trade (GATT). This treaty was aimed at promoting liberal economic principles, such as non-discrimination in trade, support for foreign enterprises, preferential access to developed markets, and so on. In short, the GATT was essentially a series of multilateral trade negotiations, with an aim to stimulate international trade by lowering trade barriers. The correct answer is D.