Lelouch declared the creation of the "United States of Japan". But why did he add "United States"? Japan is not called this in the real world, nor in the series before this moment. Why did he have this change of mind?
I am in the middle of R2 but I will not mind spoilers from manga or further episode if necessary.
It is used as an artifact to show Lelouch's interest in freedom and democracy and all that stuff we usually associate with the "United States" image. And I am not talking about USA. In our world, there are/were a lot of countries that used the term "United States" in their name.
In Code Geass universe, there are no USA (now I am talking about THAT stars and stripes real world nation).
the duke of Britannia bribed Benjamin Franklin to betray Washington, and the rebellion failed.
Then Britannia loses the british isles, and relocates to the New World.
in 1807 AD, Elisabeth III is captured by a revolutionary militia and is forced to abdicate. She and her knights move Britannia into the new world.
But Japan has massive sources of Sakuradite, a scarce resource in the west.
Sakuradite is known since the middle ages, but its too scarce in the west. Marco Polo in his travels learns that Japan has huge deposits, and this knowledge spreads in the west.
So in order to fuel the war machine, it is vital for Britannia to hold unto Japan.
Since Britannia holds (at the time of R2) almost all of the world and it is a monarchic Empire, Lelouch wants to declare at the same time his rejection of the government system of his father, and his intent with building a free nation.
Lelouch's intended style of government is unlike real-life Japan's central government, in which all laws and decisions pass from the decision-makers down to prefectures which do not make their own differing laws. To add the words "United States of" is to communicate that, of all the types of government that exist (such as confederation, empire, federation, hegemony, unitary state, etc.), he wants to avoid Japan's constitutional monarchy system and select not only a democracy (of which many varieties exist), but specifically Federalism: "a political concept in which a group of members are bound together by covenant . . . with a governing representative head. The term "federalism" is also used to describe a system of government in which sovereignty is constitutionally divided between a central governing authority and constituent political units (such as states or provinces)." This fits with Lelouch's action principle that the king should consider himself like only one piece on the board of a chess game and that the other pawns are also valuable.
In the real world, Japan is a constitutional monarchy (formerly an empire) comprised of prefectures, which are administrative divisions called unitaries ("governed as one single power in which the central government is ultimately supreme and any administrative divisions [subnational units] exercise only powers that their central government chooses to delegate"). Since prefectures directly follow the decisions of the nation's central government, this differs in nature from a federated union of states.
The real-life United States of America is a federal government, meaning "two or more levels of government that exist within an established territory and govern through common institutions with overlapping or shared powers as prescribed by a constitution." The word "federal" refers to a federation or group that retain individual rights: "entity characterized by a union of partially self-governing states or regions under a central (federal) government." It was designed in such a way that federal power is supposed to be balanced by states' individual powers and the will of individual citizens (an actual union of colonies that started out with differing charters and laws but which decided of their own will to become a team against the British Empire). The USA's "founding fathers" were very keen to make sure that a federal government of the union of states would not easily be able to make top-down decisions, and made provisions so that state laws are still in many ways independent of each other ("created to limit the federal government from exerting power over the states by enumerating only specific powers"). Nowadays, many people rattle off the phrase "United States of America" without thinking about the meaning, but the name was chosen intentionally, to enduringly show that it is not a single entity nation like many others but rather a conscious, willful union (banding of) individual states that largely intend to maintain their autonomy even while forming a team. This is the message that Lelouch wants to convey, and therefore the United States of Japan is referred to as a Unitary Parliamentary Democracy (not a real-life phrase).
