A Key Event

The Battle of New York, also known as the Attack on New York, the Attack on Midtown Manhattan, the Manhattan Crisis and the Incident, was a major and decisive battle during the Chitauri Invasion in Manhattan, New York City, in which the Avengers were able to defeat Loki and his Chitauri army, and thwart his plans of subjugating Earth.
According to Loki's plan, the Battle of New York was to be the first of many attacks in his quest to subjugate Earth, but the actions of the Avengers stemmed the invasion before it could spread. The Incident is considered a monumental event in human history, and publicly confirmed the existence of extraterrestrials to Earth's citizens.