The world's five major religions were literally thousands of years in the making. As the video above by Alex Kuzoian for Business Insider shows, Hinduism, Buddhism, Christianity, Judaism, and Islam often took root in a small geographical area and then spread like wildfire to surrounding regions — and sometimes continents.
Some of the biggest shifts occurred through government endorsements of certain religions and, occasionally, conquest. Christianity first spread in Europe through the endorsement of Roman Emperor Constantine, and in the Americas and Africa as European colonization took hold. Islam similarly spread through the conquest of much of the Middle East and northern Africa by Mohammed and his followers.
Government-led conversions also played a role in the spread of east Asian religions. In the Mauryan empire (in modern India) during the third century BCE, Emperor Ashoka the Great was troubled by the effects of war and conquest, and converted to Buddhism. According to Buddhist teachings, he then helped spread the religion — not just in his empire, but surrounding territories — by sending missionaries around the world to disseminate its teachings. The effect is shown in the video above, as Buddhism picks up not just in India, but in Nepal and eventually China, Japan, and other areas as well.
So while the idea of government-sanctioned religion is now rejected by much of Western society in favor of religious freedom, the practice played a huge role in what many of us believe today.