There will be lots of wars in the future because of the spreading atheism. Militant atheists (for example: Mao, Stalin) are known to be the most blood thirsty savages ever seen. The more atheists there will be, the more war and chaos they will bring with them.
Most of the wars in the history of the world were made for religion. The reasons for wars are known. There are wars for religion, race and energy sources.
But I do not find it right to group people according to their beliefs and ideologies. To me, there are good and bad people. It is possible to find good and bad people in every belief and ideology.
Atheist, Christian, Muslim, Jewish, etc. it does not matter. For all there are good or bad people. It's not true to make generalizations.