John Green discusses early Islamic history and some of the beliefs of followers of the religion. Like Christianity and Judaism, Islam is a monotheistic religion and has religious texts, most notably the Quran. John some of the themes of the religion: strict monotheism and the importance in taking care of others that are less fortunate. Also, he covers the Five Pillars of Islam: Shahada, Salat, Sawm, Zakat, and Hajj.
John Green explains the history of Buddhism and how Siddhartha Guatama, or Buddha, set the foundation for the religion. He briefly discusses Siddhartha's life as a prince and how he became Buddha. John then describes the Four Noble Truths, the essence of Buddha's teachings, and gives a glimpse into the life of monks following the religion. He touches upon how the religion spread and was particularly attractive to low-caste Hindus.
John Green discusses how Jesus spread Christianity using his public image of being considered the Messiah. He also mentions a couple of historical reasons for Christianity becoming a world religion: The Jews opening up their religion to non-Jews, and Saul of Tarsus (Paul the Apostle) actively spreading Christianity throughout the Mediterranean.