assuming it wasn't a nuke, 95%+ of non-english would flee london it were subject to a sustained attack. nearly all of them aren't there because they love british culture so damned much they left the country of their birth. they're there for the gibs and other economic opportunities.  let the money stop flowing or make it too uncomfortable/dangerous, and they would scurry somewhere else. and that's why you shouldn't allow any sort of mass migration. they're not loyal to the country, not interested in assimilating. when it's all said and done, they're opportunists; noxious humanoid pigeons who settle wherever it's most convenient. there is no deep attachment to the culture, the land, the native population, and that's ultimately what's most awful about mass migration. strangers coming into your home, telling you to accommodate them, until they outnumber you. squatters on a national scale.
United States