The major DNA divide within China is along a North-South divide.
Mix of Han people from the Yellow River with a lot of Northern pastoral tribes
Speaks Mandarin, which has heavy influences from Northern pastoral tribal languages
Closer to purely Han people from Yellow River
Speaks Cantonese, Hokkien, and other languages that Tang dynasty poems rhyme in
Northern Chinese are also taller, although this isn’t dichotomous–height is a continuous increase as you move from the southernmost to the northernmost. (True anywhere in the world as the temperature gets colder)
That is a pretty incorrect description of the DNA make up of Southern China.
In almost all regions, the maternal mitochondrial DNA mostly stayed the same, meaning it did not get replaced, however, the paternal Y chromosome is largely displaced. It means that when migration/invasion happened, the native male population got a gender specific genocide. So paternal lineage that would have been local to Northern China is now dominant in Southern China, and paternal lineage that would have been local to Southern China, is now more numerous in South East Asia.
That is like every country plan whatsoever.
Americans do that to marginalize the Native Americans in early days.
Australian do that to marginalize the Aborigines until few decades ago.
All Central/South American countries do that to marginalize the natives.
Nazi Germany do that in Europe.
Liberia do that by spreading out the liberated African American to marginalized local African natives.
Soviet government sent Russian majority to marginalize various ethnic minority republics.
Chinese government sent Han majority to marginalize various ethnic minority.
It is never a CCP specific strategy. People of all colors have done that all the time.
The ones that keep it to themselves….
Apartheid South Africa.
It has. South of the Yangtze was dominated by Kra-Dai, Hmong–Mien and Austroasiatic speakers. Now, if they still remained in the region, they are extreme minorities compare to speakers of the Sinitic languages. Even early Sinitic migrants were later forced to change their language by waves of later migrants from the North. Just look at Taigi, with Middle Chinese imposed above the Old Chinese substrate, and now nearly completely killed off by Mandarin.
Since the Sinitic language family is a sub-branch of the Trans-Himalayan langauge family, the original Sinitic speakers were based in Sichuan, before moving into the Central Planes. In the North, they were constantly challenged by people moving East from the Asian Steppes, and original Dongyi inhabitants living along the coast. As for which route they took to get to Sichuan is up for debate, although I think it’s more likely that they migrated across the Himalayas into Tibet before getting to Sichuan.
The theory pushed by China is that Trans-Himalayan languages moved from Northern China towards India, however, intra-family diversity is clearly much higher away from Northern China.