Here's a few notes to clear up some misconceptions that many seem to have.
The flick was NOT ever intended to be an accurate portrayal of New York gang life, although there were some realistic elements. At the time it was generally accepted that it took place in the future, although nothing in the movie supports this. At best it can be considered an urban fable that takes place in a sort-of-imaginary world. You know, like Pulp Fiction (do you really think 90's LA gangsters dressed like that??).
Second, the film itself was not accused of inciting violence. Problem was, it was a VERY popular film with gang members, who would show up in force. Two rival gangs would show up at the same theater, and... you can figure the rest out yourself. One guy was killed on the first weekend the movie was playing in New York; after that, the distributor hired off-duty police for security at every theater across the country that showed the flick. In many places in US, this served more as advertising hype than anything else...
Finally, it was widely known back in the day that The Warriors was based on the ancient Greek nonfiction tale Anabasis, written around 370 BC by the Spartan general Xenophon (it's also published under the title The Persian Expedition). In this classic tale, a battalion of 10,000 Spartan mercenaries join the Persian emperor Cyrus for a war in Asia Minor (i.e. Turkey). Cyrus's army is defeated, the Spartan leaders are captured, and the remaining force must make their way across country, fighting various hostile tribes along the way, experiencing their own internal power struggles, until they reach the safety of the sea. I'm shocked that no reviewer seemed to be familiar with this; in the 70s almost nobody talked about the movie without mentioning it.
Great flick, by the way, and it holds up extremely well over time. I'm sure the remake will suck.