Snap

"Little one, it's a simple calculus. This universe is finite, its resources finite. If life is left unchecked, life will cease to exist. It needs correction." "You don't know that!" "I'm the only one who knows that. At least, I'm the only one with the will to act on it."

- Thanos and Gamora

The Decimation was what followed as Thanos successfully gained all the Infinity Stones and activated them in the Infinity Gauntlet, wiping out half of all life within the universe.

Background
"The entire time I knew Thanos, he only ever had one goal: To wipe out half the universe. If he gets all of the Infinity Stones... he can do it with the snap of his fingers, just like that."

- Gamora to Thor

To be added

Destruction
"Oh god..."

- Captain America

To be added

Aftermath
To be added