It has been 72 years since the last World War ended. No one is in a hurry to start a new one. Each and every country has their own advantages and disadvantages. That includes China as well. Imagine a military confrontation between China and the United States (let's say, over Taiwan). The Chinese weaponry is no match for the advanced American equipment. Even if Russia decides to enter in to an alliance with China (very unlikely), it is going to be tough for the Chinese.