Original sentence: Christianity encompasses numerous religious traditions that widely vary by culture, as well as thousands of diverse beliefs and sects; over the past two millennia, Christianity has been grouped into three main branches: Roman Catholicism, Eastern Orthodoxy, and Protestantism
Edited sentence: Christianity encompasses numerous religious traditions that widely vary by culture, as well as thousands of diverse beliefs and sects; over the past two millennia, Christianity has been grouped into three main branches: Eastern Orthodoxy, Roman Catholicism  and Protestantism