Political System
The Imperial Federation is categorized as a federal monarchy, with the current Monarch as Head of State. The various component states have their own government which then elects a representative to sit in the Imperial Council on the Citadel.
Head of State
Since the Imperial Federation was founded by Humans before their space age, the Head of State is the concurrent Emperor or Empress. When Earth was united for the first time, Federico XX renounced most of his previous titles so that everybody would know him and his successors as 'Emperor/Empress of Mankind'.
According to the Constitution, the monarch has 3 main offices:
Supreme Commander of the Armed Forces: They can order the deployment of the Armed Forces wherever they like inside the Federation and authorize undercover operations, but they can't declare war without the consent of the Council and the Imperial Parliament. By contrast, the Parliament cannot employ the Armed Forces without the consent of the monarch.
Head of the Foreign Office: Among the Humans it's believed that it's necessary to give the monarch the necessary powers to keep an eye on external threats and engage in diplomacy independently. The Monarch and the Government have to agree when signing treaties with foreign nations, but the monarch can engage in personal talks with foreign officers at their discretion.
Guardian of the Constitution: A thorough knowledge of the Imperial Constitution is paramount when designating an heir. After witnessing the rise of totalitarian regimes in Europe in the 1930s through faults of democracies, this role has become even more vital in the Federation, as the monarch makes sure that no political party tries to pass laws that favors only a part of the population or discriminates some.
While the system is incredibly vulnerable to abuses of power, the Vignoli dynasty so far has always proven capable of grooming Emperors with enough sense of duty to prevent any authoritarian drift in their favor.
The monarchy is also a very popular symbol, especially among the Humans, providing a commonly beloved paternal figure that improves the overall stability of the Federation.
The monarch is also the Head of State of the proper core territories of the Federation, where the majority of the Human population lives. The other constituent states have their own Heads.
Imperial Parliament
The Imperial Parliament has been introduced only in 2188, when all the other civilizations of Citadel Space joined the Federation. It is not to be confused with the Imperial Diet in Rome, which is the internal legislative assembly of Earth and her colonies.
The Parliament gathers 100 representatives from each of the various constituent states, who gather on the Citadel to discuss matters considered vital to at least two of the constituents. The Parliament elects its own President every 3 years with a single term limit and tasked with moderating the sessions. The President then stays in continuous contact with the Empress to update her on the matters discussed and also forms the Government.
Such measure was decided by Benedetta IV so that all species would have equal footing with the Humans.
Imperial Council
In the beginning, the Imperial Council was formed of just seven advisors specialized in diplomacy, stewardship, etc...but with the expansion of the Federation, Benedetta decided that this would simply not do. With the Citadel Council dead after the Reapers took the Citadel and transferred it over Earth, the Empress decided that it was time to integrate that very small assembly of major powers and include all the species now living inside the expanded borders of the State.
The Imperial Council remains primarily an advisory board for the monarch, but each Councilor represents the various constituent states with their needs and complaints, so the Empress has to carefully balance their requests. It is also an insurance for the other species that the Empress would not privilege the Humans in her administration.
Matters discussed in the Council usually revolve around the three main tasks of the monarch, meaning that is usually external policy or possible internal conflicts between worlds of the Federation that the Empress is called to solve. The Council also serves as another check to the monarch in order to go to war outside of the federal borders: all of the Councilors must agree on the use of the military, but only when is the Empress who has started the deliberation. If the request for war comes from the Parliament, the Council can only try to sway the opinion of the monarch into agreeing or not.
For example, in the recent war against the Galactic Empire, it was the Empress who wanted to send a retaliatory invasion on the other side of the wormhole. While the Council approved, the Parliament hesitated for a few months, until testimonies of the cruelty of the Galactic Empire started to arrive.
Imperial Emissaries
They are plenipotentiaries envoys sent directly by the monarch to deal with matters considered very urgent, mostly diplomatic crises. The Emissaries speak with the full authority of the monarch, but what is peculiar of this position is that the monarch can take everybody they deem talented enough to deal with the situation at hand, even a civilian they know but has never worked as a diplomat.
In some cases, the Emissaries also act as police officers sent to investigate cases of corruption, but this is an extremely delicate decision to take: if the investigation finds the accused innocent, the repercussions on the monarch would be catastrophic, even forcing them to abdicate. That is why the Emissaries have not been used in this role for centuries, instead relying on state security agencies or, more recently, the Spectres.
Constituent States.
The Constituent States are the nations that populated the Citadel Space before the Reaper War, who then decided to unite under the banner of the Federation.
Each constituent agreed to put in common defense, external policy and to make sure that their internal laws respect the Constitution and the rights of sentient beings.
The Constitution is the only Human set of laws that they have to adhere to. For everything else, the Constituents are free to act independently inside their borders. In fact, they are allowed to have their own armies, called 'Regional Armies', that are only to be used for self-defense and serve as a pool of manpower for the larger Imperial-Federal Armed Forces. They also provide the industrial bases for the Armed Forces.
Among their duties, the Constituents also have to provide between 3 to 5% of their annual income to a common fund that can be used in contingencies by the monarch and the Parliament.
Sister-Nations
The Sister-Nations are alien states that are associated with the Federation but are not considered ready to be fully integrated, be it for breaches of the common values or weak economies.
Nonetheless, the Sister-Nations enjoy multiple benefits: they don't have to pay for the common fund and they are already under the protection of the Armed Forces. In exchange, the Sister-Nations have to adapt their laws on basic rights at most after four years. If they don't, they lose the association status.
If they manage to become functional states of right, the Sister-Nations then receive funds from the Federation to invest in their economy and make it strong enough so they may one day be integrated as Constituent States.
Since they don't have to 'pay taxes', the Sister-Nations are not allowed to send representatives in the Parliament or the Council, but they can still send ambassadors who may petition for an audience with the monarch.
Crown Prince(ss)
One of the most vital duties of the monarchs is to groom an heir fit to rule. In order to do that, both Emperors and Empress are allowed to engage in polygamy and are expected to have as many children as possible in order to improve the chances of growing up a prince or princess that will have the requirements to hold such an important and vital role.
The designation is strictly family-related: the monarchs usually wait until the children are old enough, then they express their desire over who should be an heir with all of them in a sort of assembly. This is important as all the princes must agree on the successor in order to avoid dynastic infighting. This tradition was introduced by Federico I.
