Rather than originating in "The Outline of History", this phrase comes from the introduction to the later "The New and Revised Outline of History". It relates to two additional books that the author is working on as a result of the success of the first.
Wells writes:
So there has now sprung from this beginning two other enterprises, which round off and complete a working statement of the general picture of our world needed by the modern citizen.
The rule is simple - if what you are referring to is singular or uncountable, you use a singular form of the verb - is/has. If it's a plural then you use the plural form are/have.
So, it's wrong. It should say:
So there have now sprung from this beginning two other enterprises...
As an aside, I think this still sounds awkward to modern ears, I'd rather go with something like:
So, two other enterprises have sprung from this beginning
However....
This is HG Wells - one of the fathers of modern fiction. A writer whose works are taught in schools the world over. Who am I to call him out on a grammatical error in one of his major works? Is there something else going on here?
We often get this wrong in speech - there's an excellent answer to a similar question about there is and there are here, so I'll not go over old ground. You'll hear this type of thing every day from journalists and (mis)usage like this often works it way into print.
But usage is also subject to fashion and I suspect that this may be what we are seeing here.
I've spent some time this morning on Google's wonderful NGram viewer playing with plural/singular verb/subject combinations and there seems to be a pattern that reflects an increased use of mixed forms between about 1860 and 1940 - Wells lived from 1866 to 1946.
This is just conjecture on my part - it's not something I've had time to research fully, but it may be that the usage referred to was, if not actually correct, then at least more acceptable at the time that it was written.