Some small dog breeds happen to be more aggressive than others. This is mainly due to their ancestral history of being hunters & guardians. Here you'll find a list of most aggressive small dog breeds.
Dachshunds are prone to aggression because of their long history of badger hunting. Yes, these little dogs are notorious badger hunters, which requires aggression to succeed.
Beagles are natural hunters. Therefore they have a high prey drive that sometimes leads to aggression. This aggression often arises around small animals.
Cocker Spaniels are one of the most aggressive dog breeds around. As a result, many of these dogs suffer from Rage Syndrome, also known as Sudden Onset Aggression.