Why do some countries ban certain dog breeds?

What dogs are banned in the US?
A number of breeds have been restricted or banned, including Rottweilers, American Staffordshire Bull Terriers (“Pit Bulls”), Chow Chows, German Shepherd Dogs, and Doberman Pinschers, and the list is growing.

Which dog is banned in India?
Doberman is a Dangerous dog but it is not banned in India but some dog breeds are banned in India. They are quite muscular and agile from the body.