Let's see, the Black Plague struck europe in the early 1300's and within 5 or 6 years reduced the population from 75 million to 50 million. The plague continued to kill people for the next few hundred years. War killed thousands more and probably most in europe didn't make it much past the age of 30. I believe in 1914 there were about 2 billion people on the earth. The Spanish influenza kill about 30 million people. Number killed was almost the same but to equal the percent killed, it would have needed to kill twice as many. Then WWI came and killed a few million more.
Hmmmm...I'm willing to bet that if you were able to interview people from each time, they would tell you they were living in the "great tribulation." Maybe the Society needs to copy right that term.