China has a very long history, so it's not quite as simple as "Ancient, Medieval, and modern," but I think there are general guidelines that can define different eras of Chinese history. I'm not an expert on this by any means, so I'm happy to let others chime in. I know I can answer your question, but it's daunting to summarize such a long history and go into the detail that this subreddit requires!

First, there are two misconceptions I'd like to address that will hopefully also give you a beginning idea on how to conceptualize Chinese history. First is that China has not always had its modern borders; this seems like an obvious thing to state, but it will be useful to keep in mind that for a large amount of the events I'll be describing, they don't take place over what we think of as China but a much more confined space.

This sort of relates to my second point -- that China has not been a continuous, united polity for much of its history. I know that when I used to imagine China, it was as a single unified government that lasted thousands of years over many dynastic changes. The truth is, China has spent a significant amount of its history divided and fighting among "itself," although that's not a totally accurate description. Several times, central government control has weakened and resulted in the existence of multiple independent Chinese Kingdoms that went to war against one another. The point I want to make is that these periods lasted for often hundreds of years, and were just as influential towards establishing Chinese society and culture as dynasties were. Famously, there is the Warring States Period, the Spring and Autumn Period, the Three Kingdoms period, and the Five Dynasties and Ten Kingdoms period. These times of disunity and war lasted anywhere from decades to hundreds of years. But, significantly, it's from these chaotic periods that Confucianism and Taoism developed, as well as being where nearly every Chinese legend and folktale you'll hear is set.

As I tried to write more of this the more I realized how much I'm really in over my head. But, I think I can still give you a reasonably accurate and helpful answer by keeping it general and focusing on what I know.

China has what I'd call a "legendary" period from which very little archaeological evidence has been gathered, but classical Chinese historians assure us were real. I think the point to take from this, however, is that even ancient China had a sense of a long and civilized history that preceded them.

From the Warring States Period (~475-221) came Confucianism and Taoism. The author I'm going to cite describes this as "a golden age of classical thought," so I think its safe for me to call this a "Classical Era." Much like how we have an idea of a "Classical Greece" where iconic historical figures and lasting philosophies emerged from, the Warring States Period to the Han Dynasty is where a huge amount of things we would consider as "Chinese" began to emerge. Like I said, I'll keep it vague to avoid saying anything inaccurate, but the Han Dynasty is when Confucianism became a government-sponsored philosophy and when Sima Qian wrote The Records of the Grand Historian of China, which set the model for how to write Chinese history for centuries to come.

From the Han Dynasty onwards we have a much more solid historical record to work off of. I've seen the end of the Han Dynasty to time of the Northern and Southern Dynasties (~220 C.E. - 589 C.E.) referred to as "early Medieval China^[1]."

Obviously I'm simplifying this, but from here until the establishment of the Yuan Dynasty (aka the Mongols) in 1234-1271, nothing too "out of the ordinary" happens. Centralized government breaks down again, is reestablished again, and Buddhism begins to spread throughout China. During the Tang (618-907) and Song (960-1234) Dynasties, China prospers immensely and is one of the richest places in the world. Although things obviously aren't perfect, architecture and poetry flourishes, woodblock printing and movable type printing is invented, gunpowder is utilized in warfare, and paper money begins to be used for the first time in the world.

Oh my lord, we've finally reached a period of Chinese history I actually sort of know about. The Mongol Conquest of China takes some time (especially for the Mongols to conquer Southern Song Dynasty) but is ultimately successful. It's one of only two periods of "foreign rule" in China's history, but despite this it was a famously prosperous period. Kublai Khan famously styled himself as a Chinese Emperor in the traditional sense, gave himself a Chinese name, and situated himself within the scheme of larger Chinese history.

After this was the Ming dynasty (1368-1644) and the Qing Dynasty (1644-1911). The Qing dynasty is when Europeans finally begin to play a direct role in Chinese affairs, and I feel it safe to call it pre-modern China. The story of the second half of the Qing dynasty is a story of slowly losing political and military influence to the West, which was finally coming up in the world. In 1756 the Canton System was established, which restricted all Western trade to a single port city in response to European traders trying to establish a presence. This eventually leads to the Opium Wars (1839-1842, 1856-1860) which marks the turning point in international relations with China and the West. In the Opium Wars, the British defeat China with superior naval power and forces China to trade with them. Britain and other Western powers (including the French, Russians, Germans, and Americans) begin to establish "spheres of influence" in China where foreigners were not subject to Chinese law and the political and economic power in China began to be controlled more and more by foreign powers.

Distaste for this among the populace in China is shown through the Taiping Rebellion and the Boxer Rebellion, which were huge popular rebellions that were vehemently anti-foreigner. The Qing government, showcasing its weakness once again, had to rely on foreign support in order to suppress both of them. This eventually leads to the overthrowing of the Qing dynasty by revolutionaries and the establishment of the Republic of China in 1912. Both Chiang Kai-Shek (leader of China during WWII) and Mao Zedong have referred to the time between the first Opium War to the overthrow of the Qing dynasty as "the hundred years of humiliation."

Then, of course, we have the rise of the Communist Party under the leadership of Mao Zedong during WWII. I think it's important to note that although Mao's Communist Party overthrew the Chinese Nationalist Party (KMT) in 1949, the idea of a Chinese national identity and national pride was extremely important to both. The beginnings of Communist China had a rough start, with things like the Great Leap Forward (1959-1961) resulting in tens of millions of deaths, and the Cultural Revolution (1966-1971) resulting in millions of deaths and unimaginable persecution and social upheaval.

The reverberations of the Cultural Revolution can still be felt throughout China and Chinese expats today, but that pretty much leads us to our maximum timeframe. Obviously today China is one of the most economically powerful and culturally influential countries in the world today.

I hope I did an alright job! I spent way longer than I hoped I would on this

Sources:
Chan, Alan Kam-leung, and Yuet Keung. Lo. Philosophy and religion in early medieval China. State University of New York Press, 2010.

Rossabi, Morris. A History of China. John Wiley & Sons, Inc, 2013.

Hing Ming, Hung. Ten States, Five Dynasties, One Great Emperor: How Emperor Taizu Unified China in the Song Dynasty. Algora Publishing, New York, 2014.