Matthew Evans - What makes a country Religious?

I've spent some time in a lot of different places and I wonder what makes people in different parts of the world religious and not so much in others? A lot of sociologist have said that people in primitive cultures tend to be more religious. While this assertion can work as a general rule, it has quite a few exceptions and holes in it. America is a civilized society, yet it is deeply religious. India is a moderately developed and educated culture and is extremely religious. People are so religious that cows walk through traffic unimpeded. Europe has generally been regarded as having a common thread of history and general ideologies. Yet religiosity varies greatly within Europe between heavily Catholic Spain and Italy with the very secular France. There theres the anomaly of deeply religious Poland which borders the Czech Republic, one of the most Atheistic and Agnostic countries in the entire world. In Poland people used the church as an escape from Soviet dominated Communism. Their Czech neighbors turned Atheist instead. How can this be explained other than by whim group think? How do groups of people come to such consensuses as a group?