Also, Chinese are not homogenous. Ignoring the 20th century Han social construct, there have always been distinct ethnic and cultural differences among differing "Chinese" ethnic groups like Cantonese, Teochew, Hokkien, Hakka, Guangzhong, etc that were erased during the Great Leap Forward and the Cultural Revolution.
Also, if you want to go the route that you are arguing, then there's a reason why Mongolia, Tibet, East Turkestan, etc fought for differing levels of sovereignity in post-Xinhai China, or that ethnic Manchus made a faustian pact with the Japanese occupation to create Manchuko. Ironically, Mao and Zhou Enlai were much more open to minorities compared to post-1980s PRC politicans.
But then again, why am I arguing with a sock puppet account based on your comment history. Either you are a very hypernationalistic commentator, or an astroturfer at worst. @Dang, thoughts about the paradox of tolerance?
The Great Wall helped, it wasn't the easiest thing to move around.
Hell, at one point in the late 18th and early 19th century, the village my family is from would have technically been Qing AND Sikh AND Dogra. Borders are artificial constructs that have historically been more fantasy than reality (at least until the late 19th to mid 20th century)