All deserts form due to very little rain or snow over long periods of time. Yes, that's right...I said lack of rain or SNOW, in fact Antarctica is the largest desert on earth. Although lack of rain or snow is the paramount reason for a desert forming, there are various factors responsible for the lack of precipitation. Ultimately, it depends on the location of the desert to decipher the reasons why it became a desert in the first place. It's all about location, location, location.