Is it what was prescribed in the Koran of muslims and what is called 'The New Testement' of christians that has given these peoples the ability to gain conversions and great swaths of land? The Roman Empire, when combined with Christianity flourished because of the roman bureaucratic organization combined with intermarraige among the conquered and probably forced conversions. Jihad, one of pillars of Islam, provided incentive to conquer lands and people. Forced conversions also surely played a part. Was it the religious tenents as they were written and followed by their adherents that caused populations of Christians and Muslims to be able to possess a lot of land, fight to obtain and protect it, therefore evolving to produce the large populations of Christians and Musims we have today?

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    Why do you measure the "success" of a religion by the number of adherents? As far as I know Judaism never had conversion of many people as a goal. Just the opposite: conversion to Judaism is intentionally made difficult. – Alex Jun 23 '17 at 10:42
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    This is a question about religion, not history. If it could be answered through historical sources and methods, the answer would be book length. Question is too broad and only marginally on topic. More likely to generate discussion than answers. – Mark C. Wallace Jun 23 '17 at 10:57
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    Missionizing religions that condemned (at one point or the other of their history) any "unbelievers", and have been state religions in several key countries during the development of the region. – DevSolar Jun 23 '17 at 10:59
  • @Alex, I absolutely don't measure the success of a religion by the number of adherents nor the land area they inhabit! Very sorry if that was the impression. I'm going to edit the question since it evoked thst response! Very sorry. :( – gamliela Jun 27 '17 at 13:39
  • @Mark Wallace. Yes, I'd love to write such a book. i'm working ona rewrite of the question considering the crits received. Thanx! – gamliela Jun 27 '17 at 13:41

It is fundamentally the result of empire-building and the conversion of "conquered" or "subject" peoples. This animated map shows the spread of religion around the world from c3000BCE to 2000CE.

Wikipedia offers this page on the Growth of Religion which attempts to explain the current, rather than historic, trends.

  • The linked video offers no discernible sources. It seems reasonably sane from the age of discovery onwards, but for the periods before that it coming from Business Insider should invite scrutiny. – Denis de Bernardy Jun 23 '17 at 18:05
  • @DenisdeBernardy The video appears to be broadly correct, and offers an easily accessible overview of the historical spread of the major (current) religions. I was going to add a few further "proper" sources, for those who prefer a little more academic rigour, but then the question was put on hold, so I didn't bother... – sempaiscuba Jun 23 '17 at 20:52
  • @DenisdeBernardy, I really enjoyed watching the video. I had not fully experienced the realization of how colonization by europeans had advanced christianity on the american and african continents; anamazing amount of land and people involved. I continue my question, and am left wondering, is it greed and desire for power and conquest of the world, more land, more people, more control, or was it spiritual vigour to convert people to certain beliefs that propel these conquests? – gamliela Jun 27 '17 at 14:17

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