It is important to make a distinction between the Chinese language as a written literary practice and the Chinese language as a spoken vernacular one. Before the Han dynasty, there was less of a distinction between Chinese as written and Chinese as spoken. During the Han, however, the specialized literary language known as wenyan developed, and became the standard linguistic medium of literati and official writings. While the written practice of wenyan has been fairly consistent over the last two thousand years, the spoken practices have generally lacked any sort of unity. For instance, we may note the cultural and linguistic differences between contemporary Chinese who speak Mandarin and Chinese who speak Cantonese or other southern dialects. Of course, Mandarin, or guoyu, is a recent invention by language reformers during the first years of the Republic of China. While Mandarin is the dominant spoken form of Chinese, the project of the Republican language reformers has not been completely successful. Today, just as back then, the linguistic divisions exist, creating economic, political, and cultural consequences.
(see a map of the Chinese linguistic groups)

the written vs. the spoken
history of written forms