I'm going to assume you're not trolling here and are asking this incredibly loaded question with the expectation of a serious answer. If that's the case, then the answer is yes, from a certain point of view, no from another. I'll point you to the North Korean Communists wanting to spread their ideology (and political control) to the South, and the same (mostly) for the North Vietnamese. Communism is atheist, and the idea of spreading it through military force was a major component of the former war, and in a more complex way having to do with Ho Chi Minh's actual ideology and how he translated that, the latter as well.

Now, that said, I don't think that any serious historian suggests atheism was the primary trigger for either of those wars, but very few will deny the urge to spread an atheistic doctrine as part of an effort to exert regional power in those cases. So, yes and no: yes, atheist nations went to war with nations permitting religion in order to spread their favored doctrine, no it was not "let's spread atheism to the irrational fundies", it was "let's advance the cause of (our nation's) workers everywhere, and oh, by the way, Jesus is bad, m'kay."

On a related note, for internal turmoil that actually involved tanks and machine guns in a couple of cities, head to China during the Cultural Revolution. Mao's doctrine of constant revolution said that everything from the old days, especially any vestiges of religion and Confucianism, needed to go, violently if need be. One source even alleges cannibalism on the part of Red Guards, although it's somewhat controversial. The whole affair is not considered a war, but the destruction and death were on such a large scale that I would love to see someone show me a quantitative difference between the two.