Unfortunately, Russian rulers, whether Tsars or General Secretaries, have conquered believer and unbeliever alike. Heck, most of the European wars have been between Christian kings, and were straightforward attempts to garner prestige and power at somebody else's expense. They were holy only in the sense that some of the sovereigns considered themselves the Hand of God.
I disagree. The Cold War, Napoleonic Wars and WWII were between atheists/nihilists and Christians, with Christians on the defensive. The Ottoman wars were between Christianity and Islam. WWI wasn’t Christian v non-Christian, but certainly was not along religious lines. Even the 30-years-war started off between Catholicism and Protestantism (sorta*), but ended up having very little to do with religion. (The largest nation, France, being Catholic but fighting among the Protestants).