How did dialects in various regions of China form at first?

Chinese is extensive and profound, but when did the local dialect in China branch and gradually evolve to this day? In fact, dialects have existed since ancient times, and I don't know when they can be counted. But one thing, after Qin unified the world, its territory expanded. Is this the initial witness of the formation of dialects? But this can't be said, because before the Qin Dynasty, the words and deeds of different countries were different, and the war that followed led to the emigration of most Central Plains immigrants and mixed with local residents. This is the original forming factor of today's dialect, right? The ancient Central Plains is the ancestor of China people. Because of the war, most Chinese immigrated to Shandong, and gradually formed Lufangyan with the local Lu people. Vietnamese was formed in countries that moved to the Yangtze River Delta. Moving to northern Fujian and the formation of northern Fujian dialect. Minnan dialect. South China Cantonese. Xiangfang dialect in Xiangjiang River basin. Anhui dialect in Anhui province. Hakka dialect in southeastern China. Sichuan dialect. Qin Fang dialect in Shaanxi and so on. However, the dialects in the north of China sometimes sound as if they can understand each other, but the dialects in the south are different. If the southern dialects never communicate, they can't understand each other. Therefore, Chinese is divided into eight dialects, namely Northern Dialect, Vietnamese Dialect, Anhui Dialect, Hunan Dialect, Northern Fujian Dialect, Southern Fujian Dialect, Hakka Dialect and Cantonese. Northern dialects, including the major dialects north of the Yangtze River, all belong to the same dialect because of the same pronunciation, centering on Beijing dialect. Fang Yue dialect includes Jiangsu, Shanghai, northern Zhejiang and a small part of northeastern Anhui in the Yangtze River Delta, with Shanghai dialect as the center. Anhui dialect includes northern Anhui, with Nanchang dialect as the center. Hunan dialect includes the northeast of the lake, with Changsha dialect as the center. Northern Fujian dialect includes northern Fujian and southern Zhejiang, with Fuzhou dialect as the center. Minnan dialect includes southern Fujian and eastern Guangdong, with Xiamen dialect as the center. Hakka dialect includes southwestern Fujian, northern Guangdong, southwestern Jiangxi and southeastern Hunan, with Meizhou dialect as the center. Cantonese dialects include Central Guangdong, Hong Kong and Macao. Focus on Guangzhou dialect.