Mandarin as a language functions as a unifying force for a Chinese identity across the country and somewhat internationally, helping to integrate and bring togetherness to Greater China. China is a very diverse country with many differing cultures, ethnicities, cuisines and even history. Although Mandarin functions as a national language it is not even a case of being linked to the majority culture or ethnicity with Han Chinese people speaking a variety of languages in the country, however Mandarin allows such diverse cultures over such a large country to communicate, coexist, and share in a common history of China.
Even though Mandarin dialects represent the majority of language used in China, both statistically and geographically, Mandarin is also actively leading to language decline in certain areas and this is not being helped by government policy of both Mainland and Taiwanese governments. In Taiwan both major parties have increasingly failed to support minority and indigenous languages which are declining compared to Mandarin. Mandarin is however directly being used as a language or a tool of oppression in Xinjiang province of Mainland China, where the police and authorities are replace the Uighur language with Mandarin in the education system to achieve cultural homogenisation of the region.
thenation.com/article/china-xinjiang-uighur-oppression newbloommag.net/2016/08/13/mandarin-problem-taiwan