This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
Q: Passage: Hokkien originated from Quanzhou. After the Opium War in 1842, Xiamen (Amoy) became one of the major treaty ports to be opened for trade with the outside world. From mid-19th century onwards, Xiamen slowly developed to become the political and economical center of the Hokkien-speaking region in China. This caused Amoy dialect to gradually replace the position of dialect variants from Quanzhou and Zhangzhou. From mid-19th century until the end of World War II, western diplomats usually learned Amoy Hokkien as the preferred dialect if they were to communicate with the Hokkien-speaking populace in China or South-East Asia. In the 1940s and 1950s, Taiwan also held Amoy Hokkien as its standard and tended to incline itself towards Amoy dialect.
A:
After the 1940's and 1950's Opium War, what became a major treaty port?