The study of religions may be divided into two distinct types of belief systems, universalizing and ethnic.
Universalising religions actively seek new members. Christianity, Buddhism, and Islam are powerful universalizing religions active in the world today. Indeed, many battles have been fought among these faiths to gain converts; witness the terrible loss of life during the Crusades when Muslims and Christians battled for “truth.” Universalizing religions usually are thought of as “religions of revelation.”
Ethnic religions, on the other hand, are not interested in seeking new members. Hindus, for example, do not actively proselytize (Hare Krishnas, no matter what they preach at street corners and airports, are not Hindus in the truest sense).
Other ethnic religions include Judaism and most forms of animism or nature worship. Universalizing religions often grow out of ethnic religions; Christianity, for example, emerged from Judaism. Buddhism grew out of Hinduism.
There seems to be more mixing of faiths in East and South Asia than in the Middle East and Europe. This is probably due to the greater religious tolerance of Hinduism in Asia. Likewise, the Chinese traditions of Confucianism and Taoism blend together with little conflict.
When the Chinese migrated to Gold Rush California in the 1850s, their “joss houses” had a curious construction of separate rooms for Confucianism, Taoist, and Buddhist worship.
It is significant to note that the large monotheistic religions appear to have been the most intolerant and warlike through historic times.
Wars on religious grounds between polytheistic societies are unknown, but since the rise of monotheistic Islam, Judaism, and Christianity, religious wars have proliferated in Europe, the Middle East, Africa, and Asia.
Europe and the Middle East have been dominated by many more exclusive religions than the rest of the world. Christianity in Europe and Islam in the Middle East not only are universalizing in the truest sense, but also are exclusive.
The longstanding ill will between the United States and some countries of the Middle East is based in part on these religious differences.