The Han Dynasty started by a peasant revolt against the Qin Emperor. It was led by Liu Bang, the son of a peasant family.
Some important inventions we made are iron casting, crop rotation, acupuncture, and invented the cross bow for safer and farther attacks. They also were high in advancements, the had medicine, mathematics, building, agriculture, engineering, and astronomy.
The expansion of the empire was the upgrades on the weapons like cross bows and iron weapons. the the upgrades, they were able to conquer other villages faster and easier.