Does the destruction of towns mentioned in Surat Al-Isra include countries like America, and are the People of the Book today disbelievers or are they still People of the Book, and is it permissible to marry them?

The ruling on the People of the Book and marrying from among them has been previously clarified.

As for the verse: ﴿And there is no city but We will destroy it before the Day of Resurrection or punish it with a severe punishment. That has been written in the Register.﴾ [Al-Isra:58], it refers to disbelieving cities that are exposed to annihilation or retaliatory punishment, not to believing cities. Annihilation is only for the wrongdoers. The qualification "before the Day of Resurrection" is an added warning and threat.

It becomes clear that any city characterized by the attributes of disbelievers is exposed to annihilation or punishment and retaliation.