The eschatological predictions in the 19/20th centuries need a proper historic contextualization.
Apocalypticism tends to rise in times of social/economic/political upheaval. In late nineteenth century, it was not hard to see that a great war would come up sooner or later; it wasn't a hard prediction to make, specially in view of the arms race in Europe. The great war was just a matter of time.
Even some political analysts themselves at the time tried to predict the year for the war outbreak. It's not difficult to understand, then, (1) that a great number of fiction novels were written in those years speculating about when and how the war would come and (2) that many religious people tried to pinpoint an year for the war/end-of-the-world in an outburst of date-setting prophetic speculation. There were so many date-setters in those years that eventually someone would get it right.
Ironically, Russel himself knew there would be a war coming up (he just needed to read the newspapers) and specifically stated that the future war had nothing to do with the end of the Gentile Times in 1914!
Neo