As we know, China is such a big country with 55 ethnic minorities. And most of the minorities have their own dialects. Besides, people from different regions of China have different accent as well. So, the Chinese government promoted Mandarin all around the country for a purpose of better communication and education from 1956.

Here are some background information about Mandarin. I hope it will be helpful for your understanding and learning.
In Chinese linguistics, Mandarin refers to a group of related Chinese dialects spoken across most of northern China. Because most Mandarin dialects are found in the north, the group is also referred to as the "northern dialect(s)" .

A northeastern-dialect speaker and a southwestern-dialect speaker can hardly communicate except through the standard language, mainly because of the differences in tone. When the Mandarin group is taken as one language, as is often done in academic literature, it has more native speakers (nearly a billion) than does any other language. For most of Chinese history, the capital has been within the Mandarin area, making these dialects very influential. Mandarin dialects, particularly the Beijing dialect, form the basis of Standard Chinese, which is also known as "Mandarin".