Sentence Correction (SC) | At the time of the Mexican agrarian revolution, the most radical facti

Could anyone please help me understand the function of ''that'' in ''the most radical faction, that of Zapata and his followers''
Does this ''that'' function the same with the ''that'' in comparison sentences and refer to faction? if so, why it is not ''the most radical faction of Zapata and his followers''?
Why bother writing in this way?

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