Generally speaking, countries that have a lot of different ethnic groups and/or introduced universal education relatively late tend to be those with more diverse dialects. Think about it: in a world without newspapers and TV, where most people live their entire lives in the same village they have been born in, and relatively few travelers, any linguistic innovation that appears in one place is going to take a very long time to travel elsewhere. Thus, local dialects tend to diverge. Universal school education slows this down by introducing a standard literary language (and, historically, often in a very forcible way). Mass media, TV especially, leads to further homogenization.