Roughly 70 percent of all Chinese fireworks entering the United States come here under the control of a Chinese businessman who has used his influence to raise prices and block competitors, leaving many U.S. executives fearful of losing access to their most important Fourth of July inventories.Ding Yan Zhong has managed the flow of fireworks for a decade through the two companies he founded, Shanghai Huayang and Firstrans International.He has broadened his empire by consolidating power in China, expanding his reach and becoming the most important player in fireworks logistics on both sides of the Pacific Ocean.Now, Ding’s control of the fireworks delivery chain is nearly complete, according to two dozen shipping and fireworks executives, more than 40,000 shipping records, numerous court documents and other sources.From the southeastern Chinese city of Liuyang, where the majority of U.S.-bound fireworks are made, producers often load their products onto Huayang trucks.