". And in these disastrous times, when the ingenuity of man has multiplied the power of weapons of war, it was possible that, without the knowledge of others, a State might try to work such a formidable engine. But the idea of a war machine fell before the declaration of Governments."

The  disastrous time is 1866, just 1 year after the end of the American Civil war (1861-1865).  It places the action in the middle of the second industrial revolution. Mass production, the railroad and telegraph, aerial observation and the even more terrible weapons made the Civil War the first modern war . The Henry and Spencer repeating rifles replacing the the smoothbore musket - fast to load, but inaccurate , reduced the classic infantry attacks to suicide missions.