The population of planet Earth has not divided evenly to all continents. Many vast areas, such as deserts, glaciers and mountain ranges, are almost uninhabited. In other regions of the planet, the population density is extremely high. 

Asia is the most populous continent on the planet. It is inhabited by over four billion people. Both China and India are nations with over one billion inhabitants. This is explained by the following three factors:

1) Both China and India are large nations in terms of surface area.

2) Their climate and soil types are beneficial for agriculture, which means that it is possible to grow enough food for even a large population. 

3) The birth rates in these nations have been high. In China, the birth rate has dropped in the recent decades.