In the West, I do believe that Christianity has been the most historically influential force in our civilization. I think that a lot of policy to this day is based around Christianity in the United States even though we are supposed to be a secular nation. I think that things are rapidly changing, but Christianity still remains the dominant force for now.
Overall no other religion has taken hold of Western Civilization as much as Christianity, Christianity has roots in almost every local community in Western Nations, I think that the Christian influence has declined somewhat in recent years but overall it still remains one of the most influential forces in Western Civilization.
It is my opinion that Christianity has been the most historically influential force in Western civilization. I feel that Christianity has been at the root of almost every religious mission to new lands in the history of the west, and is the driving force behind the establishment of the United States of America.
The reality about Christianity is that it has been the most historically influential force in Western Civilization, and it has done so through brute force and barbarism. The inquisition, the crusades etc. Christopher Columbus used to hang 13 American Indians at a time. One for Christ, and 12 for his disciples.
In good cases (such as Spain, Germany and Italy), Christianity has been the force for good. Poor people taken care of. Medicine etc. Of course it wasn't always professional as Catholic countries like Italy and Germany had dictators who hated Jews and opened a Holy War on them. In bad cases (Denmark and Britain), Deism has had major influence. Christianity is part of it mind you, but it's Lutheran Christianity, a religion that condones human rights abuses and enslavement.
No, I do not think that Christianity has been the most historically influential force in Western Civilization, because there are many other forces, such as John Locke and the belief in natural rights, that had a huge impact on the development of the modern world. Christians existed in the Middle Ages too, but other forces brought the world to the present day.