The book was highly popular in the early Twentieth Century, and Hancock is likely to have read it. In Hancock's far more extensive version, constituting no less than four books, it is the Germans who launch a surprise attack in 1920, capture Boston despite heroic resistance by "Uncle Sam's boys", overrun all of New England and New York and reach as far as Pittsburgh—but are at last are gloriously crushed by fresh American forces. From the present-day point of view, it can be considered as "retroactive" alternate history. Hancok's plot has a basic implausibility in that it assumes either an overwhelming German victory over the British, giving them mastery of the seas, or a British "friendly neutrality" and a free hand to invade America. Further, it assumes the German Navy to be capable of utterly defeating the US Navy, followed by ferrying no less than a million German troops across the Atlantic and keeping them supplied for years-long hard fighting. The experience of the first two years of the actual war, at the time of writing, already conclusively proved the Kaiserliche Marine manifestly incapable of anything remotely of the kind. In actuality it was US soldiers who—a year after the story's publication—would pour across a British-dominated Atlantic to assault Germany in Europe. However, alternate history writer and analyst Dale Cozort notes that "(...)The broad outline of the war [depicted] is so much like what actually happened between Germany and Russia 25 or so years later, in World War II, that it's almost uncanny. The Germans win battle after battle but the opposition moves industry out of their reach, builds up overwhelming superiority in manpower and strategic mobility, then cuts off the cream of the German army. Sounds a lot like Eastern Front World War II up through Stalingrad". Cozort also notes that Hancock's is one of the first fictional depictions of war to make reference to tanks. Hancock appears to have been among the first American writers to graphically describe their country being devastatingly invaded by powerful enemies—reflecting the disruption of the hitherto dominant American isolationist mindset. In later decades he was followed by a host of others depicting the US being fictionally invaded by Nazi Germany, Imperial Japan, the Soviet Union and China, as well as a considerable array of extraterrestrial aliens (see Invasion literature, Yellow Peril, Earth in fiction, "The Man in the High Castle", "The Ultimate Solution"). In effect, this subgenre went full circle with the alternative history novel "1901" by Robert Conroy, depicting a fictitious invasion of the United States by Kaiser Wilhelm's Germany in the title year, bearing quite a bit of resemblance to Hancock's work.