[Warning: This article obviously contains spoilers to Luke Cage, so turn away if you haven't gotten through the first half of the new Netflix series.]
Like the other Marvel/Netflix collaborations, Luke Cage is set firmly in the Marvel Cinematic Universe, the superhero world built from the ground up starting with Iron Man. Previous Netflix shows like Daredevil have had passing references to the various Marvel movies, but Luke Cage has a direct tie linking it to the first Avengers movie.
As Luke Cage begins to increasingly interfere with Cottonmouth's criminal empire, he looks for a way to kill the man with unbreakable skin. His solution? A "super-bullet" named Judas, made from alien metal made from the wreckage of the failed Chitauri invasion. That invasion, led by Loki and repelled by the Avengers, was the big battle of the first Avengers movie and has been a big flashpoint for the Marvel Cinematic Universe since.
We're not going to spoil if/how Cottonmouth uses the bullet, but you can probably guess that a show doesn't introduce an alien super-bullet that can kill a dude with superpowers unless it has plans to use it.
This isn't the first time the Chitauri invasion has had an impact on a Netflix/Marvel series. Hell's Kitchen was in poor shape during the first season of Daredevil because of the invasion, which directly led to the Kingpin making his move on the New York neighborhod.
The Chitauri invasion seems to weigh heavily on the minds of Harlem's residents, as the invasion (and the Avengers) were mentioned several times in the Luke Cage episodes we've seen so far. It seems the citizens of New York City aren't too quick to forget the day the sky opened up and rained down murderous aliens upon the city.
There's a few other big easter eggs and references to the other Netflix series, but we won't spoil them here (at least in this article). Be sure to keep an eye out on ComicBook.com all day for more Luke Cage coverage!