The past decade of the Marvel Cinematic Universe effectively concluded this weekend with the release of Avengers: Endgame in theaters. Quibble all you want about the value of these movies in terms of the film canon, the actual mechanics of building to a conclusion after 21 films is still noting less than an achievement. For fans of the franchise, it's a milestone, and they've taken to social media -- especially Twitter -- to say #ThankYouAvengers.