The Day the Earth Stood Still (1951)

At the height of the Cold War, a flying saucer is landing in Washington: the envoy Klaatu and his mighty robot Gort, delegated by the Federation of Planets, arrive in it to deliver an ultimatum to the peoples of the Earth to stop nuclear testing. Panicked soldiers open fire on the spaceship and injure the envoy. Klaatu realizes that the only way to come to an agreement with earthlings is to know them from the inside: he escapes from the hospital and begins his own exploration of the planet.

This film shows that people are not yet ready for contact with extraterrestrial civilizations. Humanity, deeply mired in its strife and internecine disagreements, is not capable of not only meeting the envoy from another world normally, but even more so listening to him! So far, the decision is ours. All that remains is the question of how long they will wait and whether we have enough time to reason until it is too late!