The Qin Dynasty, the dynasty of the first emperor only lasted for ~20 years, with 2 emperors. They were followed by the Han dynasty, which lasted over 400 years, co-existing with the Roman Republic and early Empire. The Han empire started ~200 BC and ended ~200 AD.
There was a long struggle for power between Xiang Yu (a noble of the Chu state) and the first Han emperor. Interestingly, Chinese chessboards use Han and Chu instead of Black and White some times.
After that, the Han dynasty spent a lot of time fighting the Xiongnu, a nomadic tribe. Near this time, the explorer and Chinese diplomat, Zhang Qian lived and went to many places, his travels being associated with the Silk Road now.
The empire was interrupted for a short time by Wang Mang, a regent who took over and established the Xin dynasty which only lasted a few years before the Han took over again. This divides the Han empire into the Western and Eastern Han.
Paper was invented during the Han empire, and it's thought of as a generally good time in economic terms.
The Han empire lasted until ~200 AD, after which it was followed by the Three Kingdom period.