We’re watching Cleopatra (1963). Joe Mankiewicz came out with a six-hour film, which he suggested should be released as two, separate, three-hour films. It wasn’t. So what was the first ‘single film’ that was released in two or more parts?
The first one that I can think of is The Lord Of The RIngs. Granted, the story was in three books; but it’s all one story.
Star Wars? No. It was conceived as a ‘1930s-style serial’. Each story was self-contained; unlike TLotR or Cleopatra.
The first one on that list is Die Nibelungen by Fritz Lang, 1924.
Back to the Future maybe? I know filming for parts II and III were combined to save money.
There was a German silent movie called The Indian Tomb, which was released in two parts in the 1920s:
I’m sure you’re looking for Hollywood movies, but from the USSR came War and Peace, released in 4 installments but bingable today on one sitting.
No, those don’t count; as they were stand-alone movies rather than a single story. Filming II and III concurrently/consecutively is coincidental.
Yes.
The first “sequel” I can think of that makes little or no sense without the film that preceded it is Laurel and Hardy’s Tit for Tat. It was released in January 1935, five months after Them Thar Hills, which gave the reason for the animosity between their two sets of characters.
I write “sequel” because it apparently wasn’t planned to be one. It was made in response to the popularity of the first movie.
From Riemann’s link, the earliest films that I would consider “Hollywood” Is Richard Lester’s version of The Three Musketeers, which he split into 1973’s The Three Musketeers and 1974’s The Four Musketeers. However, that was mainly British, so I don’t know if Johnny_L.A. would consider it “Hollywood”.
1973 The Three Musketeers was shot as one long epic film, including an intermission. During production the decision was made to release it as two separate films, resulting in 1974 The Four Musketeers. The cast however, was only contracted for the one film and paid accordingly. Per Wikipedia “This led to the Screen Actors Guild requiring all future actors’ contracts to include what has become known as the “Salkind clause” (named after producers Alexander and Ilya Salkind), which stipulates that single productions cannot be split into film installments without prior contractual agreement.”
Acceptable, as it was in wide-release in the United States. I didn’t know about this, as to me, it was one of those forgettable early-'70s films. 
Parts II & III were originally one long film, titled Paradox.
“If the western chapter of the story was relegated to being part of just one sequel instead of two, it would had to have been streamlined to a point where it would have been merely a brief episode within the story. The luxury of having ‘Part III’ allowed us to give the film more texture and make the story richer.” - Robert Zemeckis
I gather that Abel Gance’s Napoléon was supposed to have six parts, but he abandoned it after only the first. The ending of the first (only) part pretty much demands that the second follow on immediately.
Obviously it was not strictly Hollywood, but my mother (born 1919) saw the (slightly dubbed) American release as a child in Brooklyn, so it must have had a decentish sort of release in the States.
Lang did it over again in 1959 as Tigress of Bengal and The Indian Tomb (featuring Debra Paget’s notorious “snake dance”), later edited together as Journey to the Lost City.
Erich von Stroheim’s Greed was eight hours long; he suggested it be shown in two parts. The studio cut it down to two hours.
There was also the Ralph Bakshi animated LOTR. It was meant to be released in two parts but as far I know the second half was never made.
Not the first, but Jean de Florette/Manon of the Spring (1986) is all one story, and the true power of the story isn’t revealed until you’ve seen both.
It did get wide release in the US and was reviewed on Siskel and Ebert.
The original movie (1951) was also supposed to be released in two parts, but the distributors balked and cut it down to one.
Not quite what you asked, but a buddy’s father took his three boys–ages maybe 12/11/9–to see Gone With the Wind. At intermission, the boys stood as one and headed for the exit. Poor dad was reduced to running after them calling “Wait! There’s more!” Not sure whether they stayed for the second half or not–they were NOT enjoying it.
Yeah, my sister tricked me into going with her to watch a screening (Uh… Not a first release) when I was little. I asked her if it was a war movie. She said it was. OK, technically a lot of it happens in wartime; but it wasn’t The Green Berets. I’m sure she knew what I meant.
OK, that’s classic. I like your sister.
Les Vampires
While digging around for the the link on The Human Condition, I found this film mentioned on Wiki as the first film released as a serial in 1915-1916 and runs 421 minutes.
The Human Condition
Probably not the first, but Masaki Kobayashi’s The Human Condition is one of the longest. It was released in three parts between 1959-1961, but I believe it is considered a single movie and in a single sitting runs over 9 1/2 hours.