Leonardo DiCaprio has amassed so much clout in Hollywood, he can literally green-light any motion picture he wants - and after reading a script detailing immigrant gangs battling for survival in 1860's America, DiCaprio knew he had his next project - the award-winning Gangs of New York.

"I was looking for the one that really moved me, an important film that would have resonance for years to come. There weren't many scripts out there that fit that bill", says DiCaprio.

Directed by Martin Scorsese and originally planned as a follow-up to Raging Bull, DiCaprio says that he was "truly blown away by this segment of American history."

"I was committed right away, and I said to Marty, 'However long this takes, I'm there'. It's the only movie I'm going to do."

But being truly committed meant getting physical - really physical. In order to faithfully recreate the hand-to-hand combat that members of New York's infamous Dead Rabbits gang used more than 150 years ago, DiCaprio began a series of rigorous training sessions with Dominic Vandenburg, a professor of fighting styles who truly understood the bare-knuckled clashing of immigrant groups in a bloody Darwinian struggle.

"When I met Dominic, I asked him, 'Do you know anything about the gangs in the Five Points area and how they fought?' And he said, 'Are you talking about the Dead Rabbits'? Sure I do...it's hard to describe, but it's like Greco-Roman wrestling mixed with ancient Celtic -style fighting. But the main thing we worked on was the Irish-style bare-fisted boxing, a real archaic style that wouldn't work in any ring today. It's brutal"

Brutal it was. Scorsese faced much criticism about the brutality and savagery of the film's fight sequences, but DiCaprio vehemently defends the explicit use of violence in Gangs, claiming it's not gratuitous, but necessary to show the violent time in which America was really born.