As the Nigerian requires a visa to enter the US, he /she can stay as long as the visa is valid. If the nigerian has a green card, then he/she can live in the US for any period of time as it gives them the permanent resident status.
A Nigerian citizen, or any citizen for the matter, can travel any place (for the most part) as long as they have the proper paperwork and a way of getting there.
Permanent resident can apply for US citizen after live in US for 5 years (continuously and not leave the US in the period of 5 years).
at least 6 mounths and change your ID card
Very easy. As long as you are not a criminal.
It depends of where you are from, and how long you have lived in Denmark, or if you still live there. Google it.
yes as long as you were born in the U.S.
A senator must have been a citizen for at least nine years and live in the state that elects him to the Senate.
It didn't last very long
If you are an Italian citizen you can live in Italy whenever you like as long as you like, regardless of your other citizenships.
A citizen can register to vote, or not any time they want. If you are not a cityzen you may become a citizen if you have been a permanent resident for at least 5 years and meet all other eligibility requirements.
One must be a citizen for 7 years to be a member of the House of Representatives. One must also live in the state from which you are elected.
A non US citizen has rights just like any other spouse. Rights are dependent on what state they live in and how long they have been married.