By "national newspaper", I mean something like the New York Times, the Washington Post, or USA Today. If I live in Los Angeles, I can still buy a copy of the New York Times on the street that will have the same articles and pictures as a copy bought in New York, and it presumably would've been printed that morning on a press in the LA area. It's not so much the content of the articles that I was curious about, but the pictures - how did the newsroom in New York get the photos they were using to the other side of the country? Would an extraordinarily high quality fax machine have done the trick? Something more complicated, like sending a signal like a television?
I suppose a related question would be how were photos of international events brought back to be printed alongside their corresponding stories?
The Associated Press introduced Wirephotos in the 1930s, though pioneering forms of the technology go back to the 1890s or before. For decades, this allowed newspapers to get, over ordinary telephone lines, halftone images of photos taken in distant locations.
Various telegraphic technologies permitted transmission of the text to distant cities for typesetting and page makeup there, and by the 1970s this was supplanted by the ability to send a high-resolution image of entire pages for offset printing or fax delivery.
Though the New York Times had a European edition (printed a day later) and a short-lived West Coast edition from 1962 to 64, I don't believe that any US newspapers other than the Wall Street Journal attempted nationwide production and distribution until USA Today appeared in 1981.