Look .. we are all the descendants of the Yellow Emperor and
Yan-di.
Mandarin might be another dialect to you, but it is THE official
tongue of the chinese for the last few hundred years?
It is the elite tongue spoken by the chinese. In other words, if
your ancestor studied very hard and got the zhuang yuan title, he
will need to know the guan hua to converse with the officials and
emperor in Beijing. Doubt the officials or emperor could understand
southern dialects well.
Your pro-china argument is wrong. How do you explain Taiwan, which
is not pro-China, also "following" them? Official announcements in
Taiwan are still read in mandarin. Even the news is in
mandarin.