This page addresses China south of the Yangtze (Sichuan, Yunnan, Guizhou, Guangxi, Hunan, Guangdong, Jiangxi, Fujian, and Hainan) . As the study period starts, Han Chinese under the Han Dynasty controlled this region but were only beginning to populate it. Fujian, Zhejiang, and Hainan were completely outside the Chinese sphere. Note that at this time, China also ruled northern Vietnam in a similar manner, but failed to hold it or populate it with ethnic Chinese.
Fourth Centuries: The Toba invasion of North China (They founded the Wei Dynasty) created a huge refugee crisis as the ethnically Chinese ruling class of the previous regime fled south. These expatriates established their capital in Nanjing and a Chinese aristocracy took control of the south. It was only at this point that regions south of the Yangtze (now including Fujian, Zhejiang, and Hainan) started to be culturally Chinese.
577: China was reunited by the rising Sui Dynasty (their first emperor was of Hsiongnu extraction, btw.) Now the Chinese aristocracy of the south was in direct communication with China proper and new immigration took place. This trend accelerated during the prosperous Tang dynasty and Song dynasty. Thus, if your ancestors were in southern China in CE 1000, they probably had ancestors in northern China in CE 1.
1125: The pattern repeats. This time, the Jurchen (later called the Manchus) of Manchuria attacked and overran northeastern China. Again, Chinese aristocrats fled south, where the Southern Song Dynasty continued until the 13th century. The Jurchen rulers called themselves the Jin Dynasty. If your ancestors were in southern China in CE 1490, they probably had ancestors in northern China in CE 1000.
The thirteenth century: The Mongols conquered and controlled Northern China and gradually extended their control over South China, overthrowing the Southern Song. (This, btw, was the first war in history to see firearms used by both sides). The Mongol Empire (in China they are called the Yuan Dynasty) employed a multinational administrative corps (Iranians, Turks, Arabs, a handful of Europeans like Marco Polo), was truly cosmopolitan, and developed an excellent communications system. If your ancestors were in North China in CE 1490, it is likely that at least a few of their ancestors could have originated anywhere in the Mongol Empire in CE 1000. .
The seventeenth century: The Manchus conquered all of China and Mongolia. In China, they formed a new aristocratic class, the Qing Dynasty, which governed into the 20th century. Ironically this was the beginning of the end for the Manchu nation, as they were spread very thin governing a large empire and were genetically swamped by the ethnic Chinese whom they governed. At this time, the Manchu language is spoken only by a handful of elderly people. Thus, if your ancestors lived in Northern China in 1900 or 1800, their ancestors could have been in Manchuria in earlier periods.