“There was an idea… to bring together a group of remarkable people, see if they could become something more. See if they could work together when we needed them to fight the battles we never could.” The Avengers Initiative, created based on this idea, after the incidents of the Captain Marvel movie, had the ultimate goal: protecting the Earth from extra-terrestrial forces. There were a few people who fit the category, who were working towards a better future either by themselves or in one or the other organization.
Tony Stark was Iron Man by the year 2012, firmly established as a tech billionaire with a superhero side job. Steve Rogers had been thawed and was working with S.H.I.E.L.D. Natasha Romanoff was working as a spy, occasionally along with Clint Barton in missions. Bruce Banner had tried to recreate the serum originally created by Dr. Erskine, and the experiment had gone terribly wrong. He had become the Hulk, and to protect the world from himself, he had vanished off and was living in Kolkata as a doctor. Thor was… well, Thor used to visit Earth occasionally to see his girlfriend, I guess.
In 2012, Loki came to Earth with an intent of destroying it. He went all high and mighty with his mind control games, taking Clint under control and attacking various places, and finally getting his hands on the Tesseract. SHIELD had to act quickly and they lined up the above-mentioned people (except Clint, of course) on the helicarrier. Things went horribly wrong here as Loki attacked it with the help of Clint Barton. During that attack, Iron Man and Captain America had a difference of thought, Banner had vanished off after going full on Hulk mode and destroying a part of the ship. Thor had been thrown off the ship after being locked in the “cage” by Loki. Natasha was still on the ship. Phil Coulson, a great agent of SHIELD had been killed.
The group that should have come together, seemed as though it never would. Something had to bring them back together. This was achieved when Nick Fury showed those on the ship (Nat, Tony, Steve, and Thor, who had returned by then) the bloodied trade cards of the superheroes that Coulson owned. But the thing is, it was deception. Coulson never had them on him when he died. But Fury needed some adhesive to hold the group together, and that was the fact that all of them really respected Phil and his death at the hands of Loki had pissed them off.
If the Earth survived the battle of New York, attack of Ultron, Thanos and his army and held the line of defense, it was because of Phil Coulson. The world owes a lot to him because he was one of the best people in the entire Marvel Cinematic Universe. He was the reason behind the success of the Avengers Initiative. He was the agent that stood his ground while many ran. He was an Avenger.