By this point, I'm pretty sure that Disney are running the world. They have been an immensely successful mass media and entertainment conglomerate for 93 years now, and they don't seem to be slowing down one bit. In 2009, they acquired Marvel Entertainment, giving them ownership over the tremendously popular superhero movies of the Marvel cinematic universe. A few years later, in 2012, the Walt Disney Company bought Lucasfilm, giving them ownership over Star Wars.
Soon after they announced that they would not just start making films set in the universe of Jedi and Sith, but they would be releasing one movie each year. By 2016, Disney was responsible for all five of the top-grossing movies of the entire year; the combined efforts of Captain America: Civil War, Rogue One: A Star Wars Story, Finding Dory, Zootopia and The Jungle Book making over $5.2 billion altogether.
So it's not surprising to find that they want to expand into all kinds of media, and that they would need their own event to announce any of it. The D23 Expo, which takes its name from 1923, the year the company was founded, is a biennial convention where a lot of news about their upcoming releases are glimpsed for the first time.
As always, the company had plenty to reveal this year, even going as far as introducing a new way to experience the Star Wars universe.