How did India's population explode so much in the 20th century?

A quick look at this chart shows India having a relatively small population during the 19th century, yet quickly zooming past China to become the most populous country in the world in the 21st century. What caused this massive surge in population?<br><br>I can only assume it's because of the end of the British empire, but what part did they play (or fail to play) in keeping the population low?