The Arabian Peninsula does one very specific thing in the religious geography of the world: it is the birthplace of Islam, and the site of its two holiest cities, Mecca and Medina. Before Islam the peninsula was home to a diverse religious landscape, polytheistic Arab tribes who venerated a pantheon of deities and sacred stones (the Kaaba at Mecca was already a pilgrimage shrine), alongside significant Jewish and Christian communities, especially in the south and along the trade routes.
Into this world, in the early seventh century, Muhammad's preaching of the one God transformed the peninsula and, within a century, much of the world beyond it. Mecca, the city of his birth and of the Kaaba, which Islam understands as the sanctuary first built by Abraham and Ishmael, became the direction (qibla) toward which the world's Muslims turn in prayer and the destination of the Hajj, the pilgrimage that every able Muslim is enjoined to make once, drawing millions to the peninsula each year.
Medina, where Muhammad established the first Muslim community and where he is buried, is the second holiest city. Arabia thus marks a single, decisive birthplace: a region whose global religious importance rests almost entirely on the faith that began there and the sacred geography of pilgrimage it anchors for a fifth of humanity.