When filmmaker George Lucas showed a rough cut of his third feature to his friends Brian De Palma and Steven Spielberg in the spring of 1977, Spielberg thought it was going to be a huge hit. De Palma mocked it ruthlessly. “What is this Force s–t?” he asked.

The director who had spilled a literal bucket of blood in “Carrie” the previous year, and would open many more arteries in “Scarface” a few years later, wanted to know, “Where’s the blood when they shoot people?” But De Palma worried that he’d hurt Lucas’ feelings, so to prove he was still supportive of his pal, he agreed to pitch in — and rewrite (along with Jay Cocks, the Time critic and screenwriter) the opening crawl that gives us the back story of the Empire and the rebels in “Star Wars”: “It is a period of civil war . . .”

Even obsessives will likely find much that’s news to them in the new book “How Star Wars Conquered the Universe: The Past, Present and Future of a Multibillion Dollar Franchise” (Basic Books), in which author and Mashable editor Chris Taylor delivers tasty nuggets worthy of being savored, like a human sacrifice being digested in the Great Pit of Carkoon, for a thousand of years.

Taylor unveils, for instance, the origin of “wookiee” — the sound editor on Lucas’ debut “THX 1138” hired voice actor and DJ Terry McGovern, who brought along to the studio his fellow Army reservist Bill Wookey. Stoned, McGovern ad-libbed the line, “I think I just ran over a Wookey back there,” which Lucas didn’t use in the film but thought was hilarious. He wrote the word down in his notebook, changing the spelling.

Lucas also hired McGovern again: He’s the voice of the stormtrooper parroting Obi-Wan Kenobi to say, “These aren’t the droids we’re looking for.” The gig earned McGovern $200. Bill Wookey, meanwhile, never met Lucas and had no clue he was going to play a part in film history until he happened to see “Star Wars,” at which point people started assuming he was the inspiration for Chewbacca: Wookey is a hairy, bearded man who stands 6 feet 3.

R2-D2? When assembling the sound mix for Lucas’ “American Graffiti,” Walter Murch and Lucas worked with cans of tape identified as either reel (R) or dialogue (D) and were also numbered. When Murch called out, “I need R2, D2,” everyone on the set laughed. Lucas thought it was amusing and wrote it in his notebook.

The book also considers “Star Wars” from cultural, historical and thematic points of view.

Vietnam, it turns out, was a strong undercurrent in the thinking of Lucas (who was rejected for the draft because he was diabetic). Even before he made “Star Wars,” he wanted to make a documentary-style antiwar film on Vietnam that was to be called, in a title devised by his friend John Milius, “Apocalypse Now.” (The project passed on to another Lucas compadre, Francis Ford Coppola, who had given Lucas his first movie job working on the musical “Finian’s Rainbow.”)

Lucas saw “Apocalypse,” “American Graffiti” (set in 1962) and “Star Wars” as a loosely linked thematic trilogy exploring the war in Southeast Asia, the prelapsarian glory before it and the fascistic Empire-ruled aftermath (“Star Wars” was originally set in the 33rd century).

Back in a 1973 note on “Star Wars,” Lucas made clear which side he was rooting for in the Vietnam War: “A large technological empire going after a small group of freedom fighters.”

Since space operas were typically associated with low-budget ’60s junk, “Star Wars” had a rough time finding a home. United Artists rejected it, then Universal had an option that expired in 10 days. The studio never even bothered to supply an answer, so Lucas took the project to Disney, which also said no before Fox said yes.

As karma, Disney never will, in fact, own the original “Star Wars”: Fox owns the rights to it forever, while the rights to the five sequels in 2020 go to Disney, which bought LucasFilm for $4 billion two years ago.

One of the most amusing aspects of the book is when it reveals what a huge role serendipity played in “Star Wars.” Lucas initially ruled out Harrison Ford because he thought the audience would be distracted if any cast member from “American Graffiti” (in which Ford had a tiny part) turned up in his next one. Ford, unemployed, had returned to his trade, which was carpentry.

One of his gigs was at the American Zoetrope offices, where Lucas was having casting meetings.

Casting director Fred Roos wasn’t being passive-aggressive when he hired Ford for the carpentry job: The office, he said, simply needed a new door. Spotted by Lucas, Ford not only installed one, but stepped through another: into a galaxy far, far away. Imagine what a different set of films would have resulted if Lucas had gone with his second choice — Christopher Walken.