Under the United Planets, members of the Subsector assemblies are selected every two years, while the seated assemblypeople in the subsector assemblies select the members of the assembies of the Stellar sectors once every three years. Each Sector assembly selects it's representatives to the United Planets Assembly on Alfheim once every five years.
Many candidates for the subsector assemblies (40 to 65%) are independents who lack affiliation with a political party (Monotheist Party, Incarnate Party, and Freethinkers). However, the top two parties in the Subsector's assembly often join forces to elect the members of the sector assembly. In most cases where two parties join forces to select sector assembly members, it is a combination of the Monotheist and Incarnate parties. In some cases, the Incarnate and Freethinker parties join forces to elect their party members to the sector assembly.
At the subsector level, there are a large number of independents in the assembly. In the assemblies at the stellar sector level, the Monotheist and Incarnate parties represent the two largest blocs, with the Freethinkers winning the lion's share of sector assembly seats not held by the Monotheist and Incarnate parties. It is extremely rare for an independent to be elected to an assembly at the sector level.
When it comes time for the sector assemblies to select the United Planets Assembly, most sector assemblies see a coalition of the Monotheist and Incarnate parties elect representatives to the highest political assembly in the United Planets, but occasionally the Incarnate Party joins forces with the Freethinkers to elect legislators to the United Planets Assembly.
This trend regarding party affiliation, especially at the planetary, subsector, and stellar sector levels actually began under the Star Imperium. The local governments of worlds with a majority population of Asguardian Dwarfs were governed by one or more Moffs ruling one or more locally organized clans very often affiliated with Asuguardian Dwarf clans directly represented in the Imperial Parliament (the original clans based on the racial homeworld of Asguardia). Individual worlds with majority populations of Star Elves generally were governed by a single elected or hereditary Archon, with the local hereditary Archon leaders related to the families of Star Elves with hereditary seats in the Imperial Parliament. On some planets, a Star Elf Archon co-shared power with one or more Asguardian Dwarf Moffs leading local Asguardian Dwarf clans. Most of these local Moffs and Archons allied with one of the three factions in the Monarchist Party. A small minority allied with the Freethinkers.
Aliens within the Imperium tended to support the Imperium-era version of the Freethinkers or the Red Monarchists, Moderate Party or Blue Monarchists within the Monarchist Party depending on their religious attitudes (Monotheism, Incarnatism, or other religious traditions) or whether or not they supporting the mixing of religion and politics.
It must be noted when the subsector and sector assemblies were first elected, sometimes they were appointed by the local planetary governments instead of by direct popular balloting.
By Year 6000, local governments at the planetary level often aligned themselves with a political faction within the Imperial Parliament. When the subsector and sector assemblies were first elected in Year 12,870, their members often affiliated with the Parliament's Freethinker faction or one of the three Monarchist Party factions. When the United Planets Assembly was first elected in Year 12,919 as the United Assembly of Stellar Sectors, it's members routinely aligned with one of the four main factions in the Imperial Parliament.
The finally decades of the Star Imperium were plagued by the armed, intergalactic rebellion of the so-called Rebel Alliance, which viewed the monarchy of the Imperial Sovereign as fundamentally corrupt, and Monarchist Party members of all factions saw the way the "universal winds were blowing" and defected to the Freethinkers, which for the first time in history gained a majority in the Imperial Parliament, the future United Planets Assembly, and most of the sector and subsector assemblies.
After the establishment of the United Planets in Year 13,100, the Freethinkers rapidly declined so that by Year 13,125, the Red Monarchists and Blue Monarchists had reinvented themselves as religious-based parties (the former the Incarnate Party and the latter as the Monotheist Party) and the Freethinkers remained as a secular third party.