Theories About Why the Roman Empire Fell

I'm far from an expert on history, but I enjoy learning about the Roman Empire. I've read a couple of books that try to explain how it became so successful and why it fell eventually. Today in National Geographic is a summary of those who argue the environment and disease played to big role in both its success and failure.

During its long history there was some change in the earth's orientation to the sun. This has happened several times and may be happening now. This causes food production to rise in some areas and fall in others. When "Paul" of the Bible walked around starting churches were those he converted open minded because of theological arguments or because crops were failing. The Bible says people were waiting for another leader. More likely crops were not good and they blamed it on the Pagan gods. Maybe this new god would bring better crops.

The more we learn about movements of people from place to place over hundreds of thousands of years before recorded history the bigger weather looks as the big variable in where people lived and what they thought. In my field of economics, especially the branch that delves into history, there is an ongoing conclusion that peoples values including religion is heavily influenced by how they make a living, During the last few hundred years since religion has been tracked, we know that religion was more important in rural areas where there was lots of uncertainty about weather. Religion has been less important in urban areas where vocations are heavily based on business and management. I've read there were many cross currents of discontent as the Roman Empire's years wore on. New countries were added and the new people were not treated as equals to the Roman natives. Some became armed because of that.  

I wish it were possible to know more about the relationship between Rome and the Jews. The Bible presents the appointed governor, Pontius Pilate, as an important official in the Roman bureaucracy and Jesus a major problem for him. It seems likely the Jews were not that big a deal to Rome, they just owed some money, and Jesus was an insignificant figure to Pontius. 

If a few events had taken a different turn Christianity would have died early on like most other religions.