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. now we have been able to them them like, Jessica the Hippo shes 18 years old and may still sleep on the living room floor once in a while but that's not the same as domesticate them.
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?