Basically, a citizen of the United States is any person who is in possession of the citizenship, which can be acquired by being born on the territory of the US or by being naturalized. The citizens, unlike other legal residents, can choose their representatives in elections.
Yes, there were five states that joined the Union in war, but I do not think they were ten years apart.
That it was terrible and not as advanced as today.
It is the president who represents the nation and creates policies. The article deals with the formation of the executive branch.
