What Pearl Harbor and the dropping of the A bombs and the Terror Attack on the World Trade Center and 7/7 and the Election of Trump, have in common is that they were sharply definitive.

There was a day before (of nostalgic innocence), the day of (What happened, can you believe what happened?), and the aftermath where everyone discusses or argues what it all meant.

The rise of Fascism, the Concentration Camps, the current conquest of Aleppo are also definitive, but not so sharply. There are more events to choose from and each is less individually comprehensive. Which Trump rally made the difference? Was it the rise of fundamentalist Islamic preachers in the London mosques that seeded 7/7? The publication of Mein Kampf that led to the Camps? Lenin's attempted assassination that led to Stalin? The Wannsee Conference that led to the Final Solution?

A "Day of Infamy" is not that common a thing. That's why the dates themselves become a reference.