national redoubt
area to which the (remnant) forces of a nation can be withdrawn if the main battle has been lost
en-US/ˈnæʃnəl ɹiˈdaʊt/
en-GB/ˈnæʃənəl ɹɪˈdaʊt/
area to which the (remnant) forces of a nation can be withdrawn if the main battle has been lost