Spring rolls have a thin and almost translucent flour wrapper but are rarely fried, while egg rolls have a thicker wrapping and are almost always fried. Spring rolls are traditionally Chinese, while egg rolls are more of an American addition to Chinese cuisine.
Egg rolls found their place in America through 19th century railroad workers. Restaurants wanted to find a way to accommodate Chinese immigrant railworkers as well as American workers. This led to an increase in so-called "fusion cuisine" that combined American cooking methods and pallets with Chinese ideas. The egg roll was one of the first, and the most popular, results of this combination.