That's the thing about long-term plans. They're guaranteed to change. Years ago, when it was announced during a shareholders meeting that Warner Bros. was going all in with the DC Cinematic Universe, it was announced that two of the titles -- spread one year apart -- would be Justice League Part One and Justice League Part Two. After visiting the London set of Justice League and finding out how they plan to advance this particular story, that no longer appears to be the case.
During an interview with an exclusive group of journalists, Justice League producer Deb Snyder made it clear that it was always their intention to make this Justice League movie stand on its own, saying:
Later in the day, we were able to catch up with Zack Snyder and push him for clarification on this, as we believed -- up to this point -- that this movie would be the opening chapter in a two-part story. While the structure of the story probably won't adhere to a cliffhanger that has to be resolved in the next Justice League movie, it now sounds more like Warner and DC definitely plan to make MORE Justice League movies, but it's not Part Two of the story being told here. As Zack Snyder told us:
These dates and titles were announced years ago, and they stretched as far as 2020, when the studio would like to have solo movies for Cyborg and the Green Lantern Corps. But announcing hard and fast titles and release dates doesn't allow room for change and adaptation, and the storytellers sound like they are figuring out that their paths, narratively, may need to change for various reasons. One such example of a recent change is that Warner Bros. claimed a new date for what we believe will be a Solo Batman Movie, with Ben Affleck directing and starring in it. This was a reaction to the positive remarks Affleck received from fans of Batman v Superman, but the existence of said story could change what Snyder might have wanted to do in a Justice League Part Two.
I wouldn't be surprised if Marvel ends up taking a similar approach to the upcoming Avengers: Infinity War movies, which co-directors Joe and Anthony Russo recently confirmed would not carry the subtitles of Part One and Part Two. This frees them up to be standalone Avengers stories, and while they both may focus on Thanos (Josh Brolin) as a villain, it doesn't handcuff the first movie in having to set up too much content for the second movie.
Other film franchises suffered when they tried to split on story over two movies, from Harry Potter and The Hunger Games to Twilight and Divergent. The Part One movies of almost all of those stories suffered, so this is a fantastic decision by Warner Bros. and DC. And from here on out, we can refer to it only as Justice League, without the pesky Part One.