A Thread

You think that a wall as solid as the earth separates civilization from barbarism.  I tell you the division is a thread, a sheet of glass.  A touch here, a push there, and you bring back the reign of Saturn.

-- John Buchan, 1st Baron Tweedsmuir (26 August 1875 - 11 February 1940), Scottish novelist, poet, and politician, The Power-House (1916) Ch. 3 "Tells of a Midsummer Night"