Maybe it will be the imperial era still, though it doesn't make sense to me. I don't see how WW1 could not be in the industrial era. Unless they're just splitting that era up and giving it two different names.
Well, 'Industrial' era to me should be more the late 18th and entire 19th centuries, but not necessarily the early 20th. So I think that at least makes sense. 'Imperial' could work, but then it would work for earlier as well.