Shanghai, with a population of more than 23 million (with over 9 million migrants), is the largest and most developed city in China. Shanghai was the largest and most prosperous city in the Far East already during the 1930's, and has remained the most developed city in mainland China. In the past 20 years Shanghai has again become an attractive city for tourists from all over the world. The world once again had its eyes on the city when it hosted the 2010 World Expo, recording the greatest number of visitors in the event's history.