(Excerpt from Prisoners of Geography by Tim Marshall)
If China did not control Tibet, it would always be possible that India might attempt to do so. This would give India the commanding heights of the Tibetan Plateau and a base from which to push into the Chinese heartland, as well as control of the Tibetan sources of three of China’s great rivers, the Yellow, Yangtze and Mekong, which is why Tibet is known as ‘China’s Water Tower’. China, a country with approximately the same volume of water usage as the USA, but with a population five times as large, will clearly not allow that.