The so-called 'parties' (Dutch: partijen) usually behaved like factions, which were formed ad hoc, could rapidly change in composition, and usually did not have strong ideological underpinnings.
The parties were normally led by an aristocratic clan (which usually gave the faction its name), followed by patrician families, and eventually several groups from the bourgeoisie, generally organised by guilds.
These groups could often switch allegiances, names and goals, secede or defect, depending on how situations and interests evolved.
The ruling dynasties or bishops could be dependent on the support from the strongest faction in order to govern, and in case of a war of succession, pretenders were compelled to ally themselves with one party or the other to stand a chance as seizing power.
Foreign powers could interfere in factionalist struggles by providing financial or military support, and sometimes take over control of a province with the help of a local party.