There are five tribes!
"Millions of years ago, a meteorite made of vibranium, the strongest substance in the universe, struck the continent of Africa, affecting the plant life around it. And when the time of men came, five tribes settled on it and called it Wakanda."
— N'Jobu - Black Panther 2018
The five original wakandan tribes, and what they do are:
- The River Tribe - Fishing and Agriculture
- The Merchant Tribe - Commerce and Trade
- The Border Tribe - Border security (these are the 'rhino guys')
- The Mining Tribe - Vibranium management
- The Jabari - opposed Bashenga, and not aligned with the royal family
Each original tribe is associated to a location (except the original border tribe, who merged with a wider group of people but are still referred to as such).
There's a sixth modern 'pseudo' tribe called the 'golden tribe' who are all descendants of Bashenga the first Black Panther. But you can't join it like the other tribes, and I'm unclear if you become a member of this tribe on becoming a Black Panther or not.
The reason that the other tribes do not initially help is that they believe that Killmonger is the rightful king, and that T'Challa is dead. Only the Jabari, who know that T'Challa is alive, come to help.
The other groups mentioned in this answer are not tribes in the sense that they are associated to a location, or originated from the five tribes who originally fought over the vibranium meteorite.