I'm curious about how the so-called Shanghai dialect came from. Now Shanghai people are basically immigrants.

It is because there are many immigrants that the taste will change. Now you can listen to a paragraph of Mandarin when you enter Beijing. Authentic Beijing dialect is not Mandarin. Some people are fashionable again. In Shanghai, for example, it is said that because of the cessation of grain transportation in the late Qing Dynasty, a large number of Cao Gang people lost their jobs and many salt gangs. These people are not farmers. After they lost their jobs, they went to the coast in large numbers to make a living, and finally formed the place of Shanghai. When Jiangsu and Zhejiang dialects are mixed with local dialects, Shanghai dialect is formed. Just like a foreigner who comes to Beijing, he always wants to say a few words of Beijing dialect. As a result, he was not so studious, so his accent was strange. More and more people like this, but Beijing dialect is almost gone. There used to be many gangs. I think the salt gang and other gangs were all from other places at that time, and they must all have foreign accents. After their influence, their words became popular, just as black English is popular in America now, not pure English. Hum, hum, haha. Serious English is not like that.