"it" as a true/logical subject or preparatory subject

I have a difficult time to analyse "it" as the true/logical subject or preparatory subject in a article, like this sentence:

In rejecting probability, and the larger area of mathematical statistics within which it belonged, China’s statisticians discarded a large array of techniques, none more critical than the era’s newest and most exciting fact generating technology—large-scale random sampling.

From Aeon article " Counting China"

Would you please help me understanding the it refer to…