Economists generally attribute much of China's rapid economic growth to two main factors: large-scale capital investment (financed by large domestic savings and foreign investment) and rapid productivity growth. These two factors appear to have gone together hand in hand.
The Unification of China was a campaign led by the Qin king and first Chinese emperor, Qin Shi Huang (formerly Qin Shi Huangdí) to unify all of that was ancient China and to solidify his rule to all of it. This campaign was part of a war called the Warring States Period.