In this sentence: who or whom?

[ducat1base]

Is this proper English? I saw this sentence but thought maybe it should be "who" instead of "whom". Are there rules to be sure?

"A 2003 Bangkok Post article put a rough estimate of the number of trafficked women in Thailand alone, the majority between the ages of 12-18, at 200,000, the majority of whom came from the Shan State."

 

[Raymott]

Is this proper English? I saw this sentence but thought maybe it should be "who" instead of "whom". Are there rules to be sure?

"A 2003 Bangkok Post article put a rough estimate of the number of trafficked women in Thailand alone, the majority between the ages of 12-18, at 200,000, the majority of whom came from the Shan State."

It's always 'whom' after a preposition.
You might be tricked into thinking this is a subject. "They came from Shan State". But the real subject is 'majority'. "The majority of them came from the Shan State" - not "the majority of they ...."