Why did religions globalize?

One possibility is that around 100 BC the population in Afro-Eurasia exceeded one million people. As a result of increased trade and cultural interaction between people across this vast area, religions were shared. New religious systems provided the foundations for cultural communication, moral expectation and personal trust among people who met, shared ideas and did business with each other far beyond their local neighborhoods.

Historians JR and William McNeil call this the development of “portable, community religions”. The common features of these religions are: there is a founding man who usually takes the word of God; there is a key text or set of texts that define man's relationship with God; there are suggested ways of life and worship; people gather regularly to have God's word interpreted for them by an authority; and there is a path to eternal salvation through some form of self-transformation. The McNeills, The Human Web: A Bird's Eye View of World History, the McNeills argue that religion became widespread in this time period for the following reasons:

In the following centuries, urban dwellers, and especially poor, marginalized people, discovered that authoritative religious guidance, shared faith, and mutual support among congregations of believers could replace the close-knit tradition of village life (in which the rural majority continued to live) and give meaning and value to ordinary lives despite daily contact with uncaring strangers. Such religious communities, in turn, helped stabilize urban society by making its inherent inequality and insecurity more bearable.

So what they are saying is that religion provides structure and meaning to large groups of people in the same way that small, close-knit village communities do. Religion, especially beliefs shared by large groups of people, has actually stabilized cities.

These religions have been accepted by thousands of followers because they appeal to many different people from all social classes and professions. If the texts and tenets of these faiths appealed to such a diverse range of people, religious beliefs were more likely to spread along trade routes, unlike earlier village-based religions.

While many people are attracted to these early religions, they are not all the same. Each faith has its own answers to questions about humanity and each has different practices. With the exception of Confucianism, which some scholars classify as an ethical system rather than a religion, all faiths offer eternal salvation in one form or another.

Judaism, Christianity and Islam are all monotheistic, with a single omnipotent and omniscient deity. Hinduism allows the worship of many powerful gods and goddesses. Buddhism and Taoism also recognize multiple divine beings in various forms and incarnations.

All of these religions teach that human relationships should be guided by kindness, selflessness and gentleness. Confucianism in particular emphasizes public moral behavior, good governance and social responsibility.