Why does America have WMD?

Why does America have weapons of mass destruction and we go around telling other countries they cant have them? Shouldn't our WMD (weapons of mass destruction) be taken away because we are the only country in the world to have ever such a weapon? And why do we go around looking for WMD in middle eastern countries when we should look into European countries? If we really want to limit nuclear weapons shouldn't we really get rid of ours first?