I kind of have to take their word for it, because believe it or not, I didn't actually scroll through all half-million clips.
Every once in a while, something comes along that makes you remember "Oh, right! This is what the Internet was supposed to be!" The Associated Press, usually an organization that keeps a tight rein on its properties, has created such a moment by releasing an unprecedented amount of historic footage to the public via a new YouTube channel, AP Archive. Granted, a lot of those moments don't really have proper video names, aren't easily searchable, and are often just silent b-roll montages; but many of them are truly iconic moments in world history.
The AP is based in New York, but it also has access to many British newsreel videos as well, like this one of Churchill announcing the end of World War II.
Although, to be honest, it's the random ones that I'm loving the most, like this one of astronaut Gordon "Gordo" Cooper speaking at the 1964 World's Fair about how he planned to go to the Moon and "hopefully much farther than that."
It's a great clip that captures the energy and bravado astronauts embodied in the 60s, and a poignant one, because Cooper would do neither of those things. However, he will always be remembered as the reason astronauts actually get to pilot spaceships—a fact which prompted me to find this clip:
A malfunction on his Faith 7 Mercury capsule meant Cooper had to manually align the ship for re-entry (NASA's scientists had originally planned on all spaceships being on auto-pilot, which would have relegated astronauts to being "spam in a can" in the words of Chuck Yeager). By drawing lines on the window and using his wristwatch for timing, Cooper managed to angle the spacecraft at just the right angle to avoid burning up or skipping out of the atmosphere.