Does anyone know a major event that occurred during the Qin dynasty?
The Qin dynasty eventually became the most powerful state during the warring states period and they eventually took over and unifyed China under first emperor Shi Huandi.
What about during the Han dynasty?
There was the Battle of Baideng. Which was a military conflict between the Han and Xiongu in 200BC. The Han invaded but were defeated in Baideng and the emperor Gaozu had to make negotiations of peace, eventually a Han princess was given to the Chanyu to marry.
And finally, the Three Kingdoms?
Sima Yan forced Cao Huan to abdicate the throne to him and ends the state of Wei and Sima Yan founds the Jin dynasty.