Justice League: The New Frontier/WMG

The Centre was either awakened or created by a time-traveling Peter Cannon.
The overall plot of The New Frontier could be seen as a Lighter and Softer version of Watchmen's: the public doesn't trust the heroes, the heroes and the government don't trust each other, and tensions build toward catastrophe until an alien attack saves everyone by forcing them to work together. Cannon is the original for whom Ozymandias in Watchmen was the Captain Ersatz; who's to say he's not playing the same role in this story?

The Centre was created by Adrian Veidt.
It would stretch his character and the theme less, and it would still be technically and legally possible (in copyright terms). What's more, with the Keene Act, there's a precedent for Watchmen elements showing up in other DC 'verses.

It doesn't matter who created the Centre.
Because Batman will track them down regardless. He is, after all, the goddamn Batman.

The New Frontier Universe was the original pre-Crisis universe.
According to writer/artist Darwyn Cooke, the story is set in a "prime continuity" where the most of the heroes debuted when they were first published. This universe in which DC: The New Frontier takes place was the first and original universe, before Krona's experiment created the multiverse.
 * Would that have been Earth-1, Earth-2, or Earth-4?
 * Earth-Three-Quarters.
 * No, Earth-1.
 * Earth-1 already has its own established Silver Age history that differs greatly from  JL:TNF .
 * Earth ½! Earth H-2-O! Earth X! ...we love you, superhero comics, but the seventy bazillion parallel universes whose sole significant differences are the color of tights the supers wear and which year they got into the superhero biz was getting old in the 80s.
 * Just consider it an Earth 0 or Earth Prime. It was the only earth, but then "a multiverse was born!"
 * Superman & Batman: Generations also takes place in this universe.
 * The Golden Age happened in this universe too.
 * No, it's Earth-21
 * Actually according to Word of God The New Frontier is supposed to be in Original Pre-Crisis continuity, However it is only an extremely small portion of time before the creation of most main DC Silver Age comics. This was done to explain the dramatic change in differing styles and attitudes between Golden Age and Silver Age (post-WWII) comics of that era without Deconstructing the Hell out of it like Watchmen or similar comics which the other theories on this page try to list.

OK, so remember when Batman's kicking the crud out of those cultists who are trying to sacrifice a young boy to the Center? The kid's Billy Batson.
He bears a resemblance to the other DCAU incarnation of the character seen in the Justice League cartoon, and the cult seems to have been careful to make sure he's unable to speak. One good "SHAZAM!" and they're so out of luck. Who could make a better sacrifice for your deity than the physical embodiment of another god? The Center wants all folks with superpowers killed; you've gotta figure that Captain Marvel's near the top of that particular list.
 * But the kid seems genuinely afraid of Batman and has more than enough time to Shazam himself after Bats removes the tape over his mouth. Of course, his appearance could be a reference to Captain Marvel, but we all know that the DCAU never does stuff like that.
 * Everyone's afraid of Batman. Even the good guys. But if you already know he's Batman, and you're a good guy, you ought to know better than to fight him. Especially if you are reliant on unfairly illegal superpowers and he isn't.
 * Or, it could be that he hasn't become Captain Marvel yet, or he hasn't fully realized gotten used to being Captain Marvel but the cultists realize that he will one day, due to his proximity to Shazam (the wizard).
 * Or, he simply was new at the whole superhero thing, and was scared by Batman, like most 10 year old children would be.
 * The boy is blonde, not dark-haired.
 * Not a problem. The cult who kidnapped him dyed his hair to make him less recognizable from his "have you seen me?" milk-carton pictures (or whatever they did in the 50's for missing kids). It's a Real Life kidnap tactic that was used frequently in the Cold War when dissidents were "disappeared".
 * Besides, in at least two alternate continuities, Billy Batson is black. So why not blonde?
 * True. But this universe is supposed to follow the original continuity of the DC characters. Captain Marvel was seen with black hair. Though, Billy's CM form is suppose to resemble his dad, who has black hair.
 * In the original continuity, there was no Center, no in-universe beef against superheroes by the government, Martian Manhunter did not look like a grown-up E.T. in his native form, and Wonder Woman did not have an adventure involving rape victims in Indochina in The Fifties—she was too busy fighting Egg Fu and the like. The New Frontier is meant to evoke the style of the early Silver Age, not to be a carbon-copy of it.
 * In the original continuity CM wasn't even part of The DCU. Fawcett wasn't sold to DC until 1971, and their alternate universe wasn't made part of the mainstream DCU until Post-Crisis.
 * Billy Batson appears in a scene from the book that was not adapted into the movie, but he still looks completely different from the kid the cultists had. Maybe he's "Hill Billy" of the Lieutenant Marvels?
 * I believe it.

Nite Owl (whoever's bearing the name right now) will team up with Batman.
Sure, why not?
 * That would be Hollis Mason, the first Nite Owl.

The Centre is a White Martian.
In The DCU, currently at least, the White and Green martians were a single species that split. In New Frontier, maybe the shapeless and telepathic life of Mars merged into a singular being, who was so powerful and dangerous that it was split by the Guardians or some other Powers That Be—there's only one Green, who, influenced by humans, becomes the Martian Manhunter, and the other result of the split goes insane without its ""good side" and tries to divide back into an entire world ecology.

Captain Marvel is this universe's equivalent of Doctor Manhattan.
Based on the Peter Cannon/Adrian Veidt speculation further up.

First, consider: in works of fiction, time passes for characters either at the same rate as the real world (for, say, television), at a slowed rate (Comic Book Time), or not at all (Mickey Mouse). New Frontier patently takes places in a same-rate-as-the-real-world world.

Now, Billy Batson became Captain Marvel at the age of 10 in 1940. But he was still 10 in 1960. He may go on being 10 for the rest of his life.

Plus, when the massive monster that's supposed to "fix" public opinion strikes, where was Cap? On the Moon, discussing the philosophy of action and why sometimes it's better not to.


 * Shouldn't it be Captain Atom?

There is a massive Nazi conspiracy.
Just 'cos. Plus they can have their asses kicked by the Freedom Fighters.
 * You mean, the Nazis caused the conspiracy against costumed heroes? Vandal Savage himself may have worked with the Nazis during WWII, in addition to being involved in the McCarthysm.