Here is a proposition that may seem self-evident to many people: As societies become more modern, religion loses its grip. People separate their religion from their institutions and from parts of their lives.
Sociologists have a name for this idea. They call it the "secularization thesis." Now, research suggests the story is more complicated.
In 1822, Thomas Jefferson suggested an early version of it, predicting that Unitarianism "will, ere long, be the religion of the majority from north to south."