It's stated in the passage that until World War II ……………

The demand for vegetable oils, which are produced from plants found all over the world, has risen dramatically over the past 100 years, in parallel with the rise in prosperity and the discovery of new uses. The pattern of production has also altered markedly, with the United States changing from being a net importer to a net exporter, as a response to being cut off from supplies from China and Indonesia in World War II. Nowadays, vegetable oils are used, either partly or entirely, in the manufacture of a wide range of products, such as margarine, soap and paint.