June 28, 1914. Probably the saddest anniversary for the human race.

[Benton D Struckcheon]

39. Not to diminish that,

but that was one of the many events set in train by today's anniversary.
The thing is, even the people alive at the time realized the importance of what had happened. Not on this date, but when the consequences began to become clear in August:

I had two short talks with Grey during the "twelve days." I ran into him on the stairs of the Foreign Office on Saturday, August 1st [...] I saw him again late in the evening at his room at the Foreign Office on Monday, August 3rd, and it was to me he used the words which he has repeated in his book, "The lamps are going out all over Europe, and we shall not see them lit again in our lifetime." We were standing together at the window looking out into the sunset across St. James's Park, and the appearance of the first lights along the Mall suggested the thought.

He was a little off: when all was said and done, large parts of the inhabited world across the Eurasian, not just the European, continent were reduced to rubble. The Holocaust was the event that killed more people than any of the others, and did so with industrial deliberateness, but the grand toll in lives was many times the number taken by it, as hard as that is to imagine.