Kinda easy when post 1880, you say every year is "the year".
First an foremost, they have NO business trying to guess a date they're already told no one is to know. Since its Adventists roots, they have been trying to predict the time of "rapture". Considering the "rapture" didn't happen as Russell falsely prophesied, they switched it to an unscriptual INVISIBLE enthronement. Where the hell is that in the Bible again!?!
As for WWI, it may have been a terrible war in modern times, but it isn't the worst war or even the first worldwide war. It was nothing but another war between Europeans. Greece and Rome went all over the known world warring. Before them, the Assyrians and Egyptians. After them the European conquests of the Continents.(Now these were actually worldwide)
Also, too, the Gentiles Times have not ended or are the GB members Jews? The most powerful nation on Earth today Israel or the Gentile USA?
The problem with trying to interpret Biblical knowledge is European thought. It's a Middle Eastern text. Those were not Europeans in it or writing it.