Bogleheads:Sandbox

Box-header is causing the table of contents to insert an extra blank heading. Navbox will work in place of HTML

Q1. using
 You are a US citizen by birthright if you were born in the US or born outside the US to one or more US citizen parents. If not a citizen by birthright, you can become one through a process of naturalization.

Once you are a US citizen the only way you can shed this is by renouncing your US citizenship at a US consulate. To do this you would generally need to have another citizenship besides US.