That was certainly part of it, as was the industrial revolution, but consider the auditorium building built by sullivan in 1889:

https://en.wikipedia.org/wiki/Auditorium_Building_(Chicago)

There is still a strong connection with the historical aesthetics in it. The lead up to WW1, in the edwardian era, featured a move towards stripped down classicism, but the real break in my mind happened during WW1/2, and particularly post WW2.