Firstly, we need to look at the time tables of history.The period we are speaking of is (in my humble opinion) a rather wider one than is generally thought to encompass the Golden Age of Illustration. I tend to place it between the Post-Civil War Period [roughly 1865] through the end of the Art Deco Period or (again, roughly) just prior to WWII, or 1940. The 1940 date is a bit of a stretch for some 'purists' of the Golden Age, but I will leave it there, for my own satisfaction and explain to you why I did so. Then you may make up your own mind. Multi-media is the key.
When we look at illustration of today, what do we see? When is the last time you actually looked at an illustrated book? Perhaps not too long ago for some, but for most it has probably been a while. We rely on mass communicative resources these days; TV, radio, the internet in particular, a myriad of periodicals, etc. We think nothing of seeing the cutting edge technologies on these wonderful tools we have to communicate with.
The difference is, that there was no difference during the days of the Golden Age of Illustration.They too were using the most advanced forms of communication that they possessed. Craftsmanship played a huge role in this. The styles of the Arts and Crafts Movement were influential in the quality of the workmanship involved in the printing of many books during that particular 'sub-period' (1880's — 1915 or so). This was probably the highest point of the Art of Illustration, as the style of the Arts and Crafts Movement delicately blended with the Aesthetics Movement and was interlaced with the Art Nouvaeu style as well.
This was a transitional period for the world in general, as we were on the heels of the Industrial Revolution and the American Civil War, and just entering the Age of the Machine. Art Deco with it's geometric rhythms was getting ready to take over and change the way the world conceptualized itself.
That was what I ment earlier when I said that it may be a bit of a stretch to include the years up to the 2nd WW. I was speaking about the new technologies; radio in particular. The printed illustration was becoming less important.Soon we would go back to the visual form of illustration, but in a much changed form....television.