Grammar problem in a sentence

I want to know the grammar of the following sentence. I can't figure out the subject.
Over the years, attempts to convert people to a particular faith have taken many different forms, most of them involving brute force and threats of violence.
Is "attempts to convert people to a particular faith" the subject? But "attempts" is verb, which means the sentence have two verbs(attempts and have taken).
The second question is why the writer can add coma after different forms and then add a noun phrase(most of them ...) .
Thank you in advance!