In regarding ancient Chinese dynasties, let's compare the Shang and Xia dynasties to the Qin and Han dynasties.
The Shang and Xia dynasties were alike in that they did not have an emperor, strictly speaking. The Qin was the first, with emperor Qin Shi Huangdi (lit. "the first emperor") ruling monarchically; the Han followed after his death.
The Qin and Han dynasties both established important precedents for modern China. The word "qin" was adopted into the name of the country (the native Chinese call it zhongguo 中国.) And the major ethnic group in China calls themselves the Han Chinese in honor of the dynasty. The Shang and Xia were too short-lived to have done so.
