What role did the three great immigrants in the history of China play in the formation of Chinese dialects?

The influence is that the original Mandarin (Yayan) has become a southern dialect. Southern dialect is a language that retains many sounds of Middle Ages and even ancient Chinese, among which Hakka dialect is the closest to ancient Chinese, and Minnan dialect and Cantonese are the closest to ancient Chinese in Sui and Tang Dynasties. Then what used to be the dialect of a few Han Chinese in the northern army of the Yuan Dynasty became the mandarin of the same age now.