Orc politics is a slightly chaotic mess built up around the race's concepts of individuality and honour. It can be roughly broken down into three levels: in-house politics, alliance politics and great house politics.
In-house politics
When the Orcs were a young race just set loose upon the world, Ratish taught those who would listen about warfare. Among the things he taught was the observation that no group of creatures can survive without the leadership of a single creature. Although later disproven when the Orcs made contact with the Tellurians , a lot of the social structure of the Orcs was built up around this idea.
One result of this is that each Orc House has a single leader - at least in name. While there have been houses attempting to follow different doctrine, these attempts usually fail due to a combination of internal struggle and external pressure. The leader of a house has power over this house, in so far as he is obeyed, which is not necessarily a given and differs between houses.
How the leader of a house is chosen and succeeded also differs between houses. For some houses it is hereditary and the only way to get rid of a bad leader is to kill him, at which point the next in line takes his place. Others have a number of families that each train a candidate and the leader becomes the winner of some kind of challenge between these candidates. Some have no real process and any member of the house can challenge the current leader for control at any moment.
Alliances Between Houses
When the amount of Orcs in the world started to grow it quickly became apparent that there were power differences between several of the houses. This resulted in less powerful houses forging alliances between each other to combat the more powerful houses.