Tell me about your world's Political Parties!

Political parties tend be depicted as monoliths, both in media and in real life. But the truth is that political parties can also be deeply layered, fascinating, and complex parts of the world. IAn irl political party like UK labour had many centers of powers, from the trade unions, NEC (National Executive Committee) and the Parliamentary party in the house of commons. While Conservatives are a sort of elective monarchy tempered by regicide.

Many political parties can be very informal, just a group of people and their supporters like many spontaneous populist parties, or they can be so deeply entrenched that they are older than even most countries.

That is to say, I am curious as to how people have worldbuilt (?) political parties in their worlds. Are they part of a democracy? A terrorist outfit? A revolutionary organization? How is it structured, its leaders, its history and all that stuff we like to yap about.