In 1970 I was an 18-year-old sailor stationed in San Deigo, California, just prior to shipping out to Southeast Asia.
Passing a sandwich shop in downtown San Deigo that advertised "Philly-Style Cheesesteaks," I pulled my two fellow sailors into the shop for a taste of something their pitiful hometowns didn't offer.
The sandwich tasted nothing like the cheesesteaks I grew up on in South Philly. I was somewhat embarassed and I told my friends that they would have to visit South Philadelphia to taste the real thing.
Since then the Philly cheesesteak has become famous and several local firms ship the authentic sandwich to other parts of the country.
Myfoxphilly.com offers a good piece on the history of the cheesesteak and you can view the video and read about the history of the famous sandwich via the below link:
As an aside, the sandwich ought to be called the "South Philly Cheesesteak," as it was first made in my part of the city.
And although Pat's made the first cheesesteak, I prefer Geno's.