If you are starting to feel as if WORLD WAR Z has been advertised for ever, you are not far wrong. Trailers first started to appear last year in anticipation of a December 2012 release, which was then delayed for six months to allow for extensive re-shoots that involved scrapping much of the original movie in favor of a new approach.
The film had been in development a long time before going in front of the cameras; nevertheless, the green light apparently came before all the story issues had been ironed out. J. Michael Straczynski’s first draft reportedly stuck close to the novel by Max Brooks, which presents its story as an oral history of the zombie war; later versions moved the film toward a more traditional blockbuster action approach.
After a studio screening of the director’s cut, a consensus quickly emerged that the ending did not work. Screenwriter Damon Lindelof was called in to revamp the conclusion – a process that involved radically revising the movie, as he explained in a Vanity Fair interview:

“I said to them, There are two roads to go down here,” says Lindelof. “Is there material that can be written to make that stuff work better? To have it make sense? To have it have emotional stakes? And plot logic and all that? And Road Two, which I think is the long-shot road, is that everything changes after Brad leaves Israel.” That meant throwing out the entire Russian battle scene—or about 12 minutes of footage—and crafting a new ending. “I didn’t think anyone was going to say, ‘Let’s throw it out and try something else,’ ” Lindelof recalls. “So when I gave them those two roads and they sounded more interested in Road B”—which meant shooting an additional 30 to 40 minutes of the movie—“I was like, ‘To be honest with you, good luck selling that to Paramount.’ ”