how china become so powerful

China's economy

China has a massive workforce.  The largest population on Earth contributes to the country's main economic strength: exporting products.  China's government pushes this with ruthless priority, and coupled with the Party's heavy investment has ushered in a wave of economic growth.  Domestic investing in new sciences and technologies encourages an ever-increasing technology sector which produces companies like Lenovo.  China's most notorious strength is in the cutthroat handling of foreign companies.  Chinese companies, backed by the government, have managed to takeover large western companies such as Volvo and Borsodchem (a Hungarian chemical company), and there have been constant complaints about Chinese companies engaging in forms of corporate espionage.

China's Military

(From the 2014 DoD report on the PRC's military): "The People's Republic of China continues to pursue a long-term comprehensive military modernization program designed to improve the capacity of its armed forces to fight and win short-duration high intensity regional contingencies."  China invests heavily in their military and is vying to be the most powerful force in the Pacific (The US Navy currently holds that title).  China performs large visible exercises such as October 2013's Maneuver 5 (which contained all three PLA navy fleets) in order to "flex" its proverbial muscles.  China is currently developing weapons specifically to shoot down American forces (if need be), and has powerful weaponry such as DF-21D Anti-Ship Ballistic Missiles and the Chengdu J20 Fighter jet.  Even the US is hesitant to provoke such a dangerous military.

International Influence

China has a great deal of international influence.  It is a permanent member of the UN security council, and this affords it the luxury of having veto authority.  China was powerful enough to enter Vietnamese waters for Oil drilling, and has received little international condemnation.  China has several powerful strategic allies such as Russia, Pakistan, Venezuela, Iran, and North Korea.  Speaking of North Korea, China is and has been the number one reason the Kims have remained in power, as they aided the North against the US-backed South Korea, and continues to have an unstable support for North Korea (mostly because they want a buffer state from Western allies).  China is quite influential in international politics, but usually is not as outspoken as the US or Russia.