Landmark in what way? WWI started in late July of that year. The 2,520 years didn't end until October. If Jesus was enthroned as King in October and threw Satan out of heaven then, how could it be said that WWI was related to that event?
A few years ago an elder told me the reason why...He said that even though WWI began in July, it wasn't until October that there were 10 nations involved. And the number "10" is a complete number. I believed him at the time.