Just a couple years ago, the world’s population reached 7 billion. This took place through a centuries-long process of growth and migration — the same process that formed the distribution of the world’s religions as we now know them today. The current result of that process is somewhat surprising in that more than half of the world’s people follow one of just two religions: Christianity and Islam. These two monotheistic religions comprise the two largest religions in the world.
Christianity and Islam both trace their origins back to the Jewish Patriarch Abraham. The biblical book of Genesis tells how, during the second millennium B.C., Abraham and his household of 80 people followed a god known as Yahweh. Abraham’s family grew into the People of Israel, who formed Judaism, the earliest monotheistic religion, and worshipped Yahweh only. Later, in the first millennium A.D., both Christianity and Islam drew upon Judaism to create new religions worshipping this same God.
Christianity migrated as it expanded. After its origins in the first century in Palestine, it became the religion of the Roman Empire. That established Christianity in the lands around the Mediterranean Sea and then brought it into Europe. When the European nations began colonizing other continents in the mid-second millennium A.D., they carried their religion with them, with the result that the population of three continents became almost entirely Christian: North America, South America and Australia. Christianity also has become the largest religion in the southern half of Africa.
After its origins near the coast of the Red Sea in the seventh century, Islam quickly moved into the Middle East and the northern half of Africa. From there it went east, colonizing the Indian sub-continent and moving farther east into Malaysia and Indonesia, which today constitutes the most populous Muslim nation.