If there was a huge and violent war between every different religion on Earth and Atheists who would win?

Alright, lets say that all of a sudden every single religious group decided that they were going to kill anyone who didn't follow what they believed. Atheists would be involved too. There are no alliances of any sort and every person on Earth will participate. Agnostics will go with whatever group they lean towards the most. Which group do you think would be victorious and why?