Point me to one civilisation or one tribe, which has not a religion, or a set of beliefs and superstitions of a similar nature used to support or enforce social order.
There are other religions beside Islam & Christianity. e.g. in Babylon, in Egypt, in India, Burma, China, Japan, ancient and modern Israel, in Australian aboriginal society etc. Show me one region, (outside of the post-enlightment Europe where a few individuals, with much influence during or after their lives, became atheists), which was full of atheists, with more of those than of the religious.
You can hardly blame Islam's and Xtianity's proselytising tactics for all those "religions".
If most religion is designed to promote authoritarian aggression and coercion (and it is), then even if a large % of people within many societies were non-believers, the public face of those societies would be dominated by the religious people who are religious largely because they seek to dominate and control others. IOW, the fact at an aggregate sociological level each society appears largely "religious" does not mean the overwhelming majority of individuals within it actually believe in anything the religion claims.
The aggression inherent to most God concepts and the epistemology of faith in general would lead to greater aggression of theists against non-believers than the reverse. Over time, this would mean a reduction in non-believers either because they were killed (and possibly genetic factors that enable non-theism made less prevalent), or because the increase level in ways in which social coercion motivates theism led more people to justify their way to belief. As principles of democracy and personal liberty arose in the Enlightenment (pushed mostly by non-believers), these social values gave protection to people from some of the coercive theist tactics, resulting in the increasing non-belief we see throughout the West.
I still think it is the case that the majority are more disposed toward theism. But their is variance in virtually all cognitive or emotional traits that would underlie that disposition. So,
its almost certain the some people are less disposed, and that use of cultural force against those less disposed is not only lesser now in the West than 1000 years ago, but was lesser 5,000 to 10,000 years ago than 1,000 years ago due to changes in the size and nature of societies and how they exerted conformist control.