Hippo's are one of natures most efficient food > weight animals, making them perfect for food. Additionally they are arguably the most dangerous land mammal, meaning they are hard to domesticate, very very hard. This, more so than other reason, is why they have never been successfully domesticated. But what if this wasn't the case?
What can I do to make my culture able to domesticate the hippopotamus? If there is something that can be done, what is the earliest it can be done? If it cannot, how close can I get?