It's a common plot device in stories for one politician to assassinate another in order to take their position. Normally though, these actions are frowned upon by everyone else and act as a motivation for the hero to avenge their politician father/brother/sister/uncle's death. In other words, assassinations are seen as extraordinary and unnacceptable.
What series of events or state of society might cause a government to not just accept that assassinations happen, but to EXPECT attempts on their life as long as they are in power?
By series of events, I mean what would have to happen for a government to accept that assassinations are a regular part of government and maintain this belief for an extended period, not a series of events such as: "We don't like the king --> let's kill him!"
Obviously, there are many short-term reasons for assassinations to be a part of government, but I struggle to think of any long-term ones. I'm talking 100 years and upwards here.
I'm searching for the type of answer like: "X was at war with Y for Z years, but because they have W type of government, they lost faith in their leader. This might have meant that Y did V...". A proper set of reasoned actions that might lead to the situation I've described.
When I tried to come up with an answer, I always came back to the fact that nobody is OK with people trying to kill them. What I need is a situation where assassinations are a part of politics just as much as rallying speeches and sending soldiers to their deaths on a whim.
In case I haven't been clear enough, let me give an example:
In Hamlet, Claudius murders his own brother and Hamlet's father in order to become king. What would have to haappen for this to be accepted as OK, and then for Claudius to be murdered, and his succersor also, and so on?