How did China's population hit a billion +?

BEHIND THE POPULATION OF CHINA :

Population growth depends on birth and death rates, till decade ago the birth rate of Chinese was quite large, though now it is minimized by the government of China, the death rate of China have been less for centuries. Geographically China was completely secure from the south side in history because of Himalayas, China is good for farming so many people concentrated on the fortile land. The land never lost a huge citizens in 1700-1900 like Rassia or Germany. So, till 2000 the the population of China is increased exponentially & it become the largest populous country in the world.