How did lui bang come to power?

In 209 BC, he held high the banner of the rebellion against the tyranny of the Qin Dynasty. After about two-year warfare, the Qin Dynasty was overthrown. At that time, Xiang Yu, the director of another rebellion group, was very angry to hear that Liu had captured Xianyang ahead of him. For the next four years, Xiang and Liu waged a war to vie for the throne, namely Chu-Han War. The war ended with the victory of Liu Bang.
In 202 BC, he established the Han Dynasty with the capital of Chang’an (Xian).