Animosity between Mandarin-speaking and Cantonese-speaking Chinese?

Ironically, people in Taiwan speak Mandarin. So "dialect" is not the cause of the PRC-ROC split. Instead, it goes back to the Chinese civil war of the early 1930s and late 1940s (interrupted by the Japanese invasion of 1937-45).

Historically, the split has been between the more traditional, orderly Mandarin-speaking north, and the looser, more entrepreneurial Cantonese-speaking south. That's where dialect may come into play (or at least serve as a proxy for more fundamental differences).

From the final comment in question, "northern Mandarin / southern Cantonese regional split" -- I believe you are looking at the North-South China divide. The Wikipedia on this is useful, but clearly short on how far this goes back in history.

There is an ancient Chinese proverb/belief:

In the South the boat, in the North the horse (Nām chuán, běi mã)"

which translates to how ancient Chinese society functioned (or should function) because of difference in geography, about 3,000 years ago, Zhou Dynasty.

The person credited with this belief is Duke Liu (公劉 / Gong Liu), an important ancestor of the Zhou Dynasty. His presence is still felt in modern Chinese society in several areas, such as urbanism, language, and poetry

In ancient China, with insufficient infrastructure and early stages of statehood, there was a difference between North and South, which was not a matter of what language one spoke, but geography:

• North: Plains (open terrain)
• South: Lakes, rivers, mountains (natural barriers)

The result of this was not just different language but something as basic as food - which still persist today (in terms of preference and staple diet):

• millet (North - Yellow River)
• rice (South -- Yangtze/Pearl River)

This proverb has morphed over the years, to encompass more than just geography, and Chinese society has developed their own (i.e. Chinese) self-perception of this North-South divide. As Wikipedia article explains, it is more a cultural difference than merely just differences of language i.e. "between Mandarin and Cantonese" of your question.

To be sure, Mandarin spoken in northern China is somewhat different than in southern China. But don't confuse it with any animosity of "Cantonese vs Mandarin".

Perhaps, a source of this confusion or stereotyping could be attributed to the fact that southern China has multiple dialects, it is therefore assumed there is animosity (between the dialect-speaking south and the Mandarin-speaking north)? (see quote below)

Additional Context: Information on 'Chinese Language'

Today: is Mandarin a language or a dialect does generate quite a few heated debates even within Chinese society (again, see quote below). The same can be said of Cantonese. Again, it doesn't mean there is animosity when they have their debates, I think it is healthy to have debates.

Finally, I am not going to write a monograph on the social history of the Chinese language (not least because I am not qualified to do so), but to give an idea of how complex the discussion of Chinese language can be -- even amongst linguists and scholars -- I have a provided a quote from Modern Chinese: History and Sociolinguistics (Cambridge, 2014), pp. 2-3 (emphasis are mine):

The major dialect groups are Beifanghua (Mandarin), Wu, Yue (Cantonese), Min, Kejia (Hakka), Xiang, and Gan, of which Mandarin is by far the largest group, with its native speakers accounting for the majority of the Chinese population.

The non-Mandarin groups are also called the Southern dialects. Each of the major dialect groups is in turn comprised of a large number of varieties that are related to each other in terms of a hierarchy with three main levels, sub-dialect, vernacular, and accent. For example, following the traditional classification, Mandarin is composed of four major sub-dialects, namely, Northern, Northwestern, Southwestern, and Jiang-Huai, all of which may be further divided into different groups of vernaculars and accents. The standard form of Modern Chinese is known by several names. It is called putonghuà ‘the common language’ in mainland China, guóyi ‘national language’ in Taiwan, and huáyi ‘Chinese language’ in Singapore.

In case you missed the first and last sentence of this quote, there's at least 4 different ways to say Mandarin for Mandarin speakers: putonghuà ‘the common language’ in mainland China, guóyi ‘national language’ in Taiwan, and huáyi ‘Chinese language’ in Singapore and other parts of Southeast Asia, and beifanghua referring to North China. Let's just say the Chinese language has a complex history!

Therefore, no -- there is no animosity between Cantonese-speakers and Mandarin-speakers, but there are debates and to term it as "animosity" is a stretch and stereotyping the North-South divide. However, there is a cultural divide between Northern and Southern China, from ancient history to today.

Yes, absolutely. Such an animosity or resentment is sure to develop when one regional dialect becomes elevated above others as a prestige or national language, as has happened with Mandarin, the speech of Beijing. Compare to southern India's distaste for Hindi.

Business Insider mentioned "fury" and "demonstrations" in response to Mandarin requirements. The Economist called their imposition "contentious". The BBC reported that some people were "refusing to speak" Mandarin.