Hi! What is the subordinate clause in this sentence?

Question

It was not until 1498, when he explored what is now Venezuela, that Columbus realized he had touched upon a continent.

 

Are there two? I thought that it was "It was...that", but I read that the subordinate clause should start with a subordinate conjunction, which in this case should be "until".

 

Thanks

Answer 1

The subordinate clause is ..when he explored what is now Venezuela.  It is a clause separated from the rest of sentence by commas that gives additional information.  The sentence stands fine without it, yet includes it. (It was not until 1498 that Columbus realized he head touched upon a continent.)  There is only one subordinate clause