The flag of the United States of America has gone through changes in history, with new states joining the union. However, where the real-life flag stops at 50, Victoria 3 flag goes up to 100.
In the most recent Developer Diary, Paradox developers working on Victoria 3 have introduced us to how flags will work in the game.
Russia, for example, has up to ten potential flag options, depending on who is in power, what kind of system of ruling is in place, etc. The Nordic countries, should they wish to enter an alliance, or a union of some kind, have different flags depending on which country is the dominant one.
At the time, though, not a lot of countries had a well-defined flag, the way that France and the United States of America did. In fact, the flag of the United States is the main point of the whole developer diary, one could say. In a question aimed at the developers, as to the amount of stars on the flag of the USA, they answered that the number goes up to one hundred, depending on the number of states.
Meaning that the number of states that can be, reasonably, expected to be part of a dedicated United States playthrough is around one hundred.
The only remaining question is, which states are the ones that enter the Union, and how well do they assimilate into it?