Yes, in the past, wars have been started solely on the basis of religious beliefs. Religion is often seen as a source of conflict in modern times; however, in an age of post-postmodernity, it is impossible to untangle the fibers of social constructs and culture that are tightly woven into our ideologies on political issues, religion, economic concerns, and world views.
Some wars were started by religion exclusively because of the biblical implications. It is a known fact that the Protestants and the Catholics found in biblical times and it was all about religion. In fact, the early colonist came to America to seek freedom of religion and chose to call themselves Puritan. Therefore wars have been started because of religious differences.
Yes, I believe that some wars are started by religion exclusively, because September 11 is a great example of that. September 11 is an important example of this, because the attackers were very clear that it was in the name of their religion that they wanted to bring death to Americans. Other wars have been fought in the name of religion as well.
If you look back at the crusades that happened, these battles were fought only over religion and not a single other thing. I think that religion probably has caused other wars to. People take religion very seriously, and will fight someone quick if they think they are following the wrong one.
I cannot believe that any religion, regardless of political or local policies of the time, would be capable of starting or promoting war. War is not in keeping with the intent of religious bodies. Religions are created to promote faith in an almighty and work for the eternal salvation of souls. War would be against every thing religion stands for.