Pb03“It was the fitting into Confucian patterns of conduct and of family and community life rather than blood kinship or ancestry which labeled one as civilized and as Chinese.”
The sentence is correct and your analysis is right. It is a preparatory subject or a dummy subject and which is a relative pronoun - at least in my terminology! It is perhaps more common to use that instead of which in sentences like this.
This structure is correct English and is used to emphasize what follows the preparatory it:
It was yesterday that the boys broke the window. (Not the day before yesterday, for example.)
It was the boys that broke the window yesterday. (Not the girls, for example.)
It was the window that the boys broke yesterday. (Not the door, for instance.)
Without emphasis, your original sentence could be written:
The fitting into Confucian patterns of conduct and of family and community life rather than blood kinship or ancestry labeled one as civilized and as Chinese.
In my analysis the original sentence has two subjects, the preparatory it and the relative pronoun which.
CB