Early American illustration has a lot of European influences. Before the introduction of photography, magazines employed numerous illustrators to attract readers. I like the early Vanity Fair covers - they're colourful with fun drawings and block colour graphics.
My journey of research for this brief begins with a lot of illustrators that aren't actually American. However, these European illustrators had an influence on American illustrators such as Howard Pyle, Maxfield Parrish and eventually the likes of Norman Rockwell. I'd never even heard of the Golden Age of Illustration until a few days ago. Not officially an art movement, it is overshadowed by advances made by American cinema.
Above is an example of a poster for the Federal Art Project in which artists including Jackson Pollock created posters for public buildings and organisations. Looking at more contemporary American illustration, the styles are very different and I'm interested to find out how the styles evolved since the 1930s. The introduction of photography and the Industrial Revolution seem to be big influences.