Six days after a protest by a group of Nazis managed to shut down a screening of “All Quiet on the Western Front” for supposedly making Germans look like cowards, the film was banned in 1930 Germany. Germany then ordered a recut version of the film that was more flattering to its side in WWI and stipulated that the cuts must be made to all prints of the movie shown worldwide, not just in Germany. Since Germany had recently been the second-biggest movie market and was expected to bounce back to the same position soon, Universal chief Carl Laemmle (a German-born Jew) meekly accepted.

Such alarming revelations, many based on newly unearthed documents, are the basis of Harvard scholar Ben Urwand’s new book, “The Collaboration: Hollywood’s Pact with Hitler.” Urwand notes that 1930s Berlin heavily censored movies out of Hollywood, which would not deliver a major anti-Hitler production until 1939.

Hollywood effectively submitted its films for approval to Georg Gyssling, a Nazi who became the German consul in L.A. in 1933 and threatened the studios with “Article 15,” which said that if an American film released anywhere in the world offended Germany, the Germans would ban all other releases from the same studio.

When top Hollywood talent including screenwriter Herman Mankiewicz (who later wrote “Citizen Kane”) proposed an anti-Hitler project called “The Mad Dog of Europe” be made independently so it wouldn’t hurt business at any studio, Gyssling vowed that Germany would ban all US films, period.

So top Hollywood execs, including Will Hays (the head of the office in charge of Hollywood’s self-censorship) and MGM head Louis B. Mayer, killed the film internally. Said Mayer (who was also Jewish), “We have interests in Germany; I represent the picture industry here in Hollywood; we have exchanges there; we have terrific income in Germany and, as far as I am concerned, this picture will never be made.”

Word got around: Hands off Hitler.

But Hollywood’s past shouldn’t surprise those who observe Hollywood’s present.

Where moviedom is heading can be reduced to a single statistic. “Iron Man,” which was released only five years ago, earned $15 million in China. Yet “Iron Man 3” has taken in over $121 million in China.

Meanwhile, studio chiefs scrambled to recut “World War Z,” which originally contained a brief hint that the zombie outbreak began in China, to mollify Chinese state censors through whom all movies must pass. China has so far rejected the movie anyway. No one knows why, and the “World War Z” grosses in China stand at zero.

The zombie flick has been spun as a surprise hit that beat expectations, but it’ll need to take in something like $600 million to break even. So far it has earned $483 million. Think Brad Pitt wishes he had come up with a scene in which brave Chinese helped defeat the zombies?

Every time Hollywood lets costs get completely out of hand, something comes along to save it. In the early 1980s it was videotapes, in the 1990s it was the DVD market. Now it’s China, but unlike the home-video market, China makes specific political demands on films. If “WWZ” is any indication, simply removing negative implications about China isn’t enough: The studios have to go out of their way to paint China in a flattering light.

Which is why “Iron Man 3” was careful to insert extra scenes (seen only in China) featuring a heroic Chinese character, why the 2010 remake of “The Karate Kid” felt like something engineered by the Chinese tourist commission (and karate isn’t even Chinese!), the 2012 “Red Dawn” remake changed its villains from Chinese to North Koreans and the disaster epic “2012” showed China saving the world.

These are merely the first few drops of rain compared to the propaganda hurricane to come, though: China will be the biggest film market on Earth by 2020, according to Ernst & Young projections. Soon, every blockbuster director who wants to stay employed will be begging for a chance to be the new Leni Riefenstahl of the People’s Republic.

What will Hollywood’s famously outspoken liberals do when a repressive authoritarian regime is essentially signing their paychecks? Nothing, of course. Don’t hold your breath waiting for Michael Moore to deliver a rant about Chinese censorship of journalists and filmmakers at the Oscars. Susan Sarandon won’t be arrested at rallies protesting China’s place as the world’s leading practitioner of capital punishment. Leonardo DiCaprio won’t be telling “Entertainment Tonight” about his new campaign to draw awareness to China’s role as the world’s No. 1 threat to the environment.

Because celebrities are very brave about taking a stand for basic human rights — but only if they can be sure it won’t cost them a thing.

kyle.smith@nypost.com