Why hasn't china became a democratic?

For thousands of years China was ruled by Emperors, but in the late 1920's the Emperor of China was over-thrown. This was called The Glorious Revolution and the man who became leader was Mao. He had the idea that there would be a world where everyone looked the same, and would follow his rules in his "little red" book. If someone didn't follow the rules they were sent to camps.
China was also an isolated country to much of the world and took part in supporting other military type actions in Asia. They supplied men and arms in the 1950's for the Korea War, and for Vietnam.
A democracy has not taken hold in China just by it's very nature and when any movement toward a democracy has been stopped.