Re: as it almost always is
Really, how are you defining that? A civil war fought between two groups of Christians (or other religious group) isn't really about religion - it's a political conflict that happens to involve Christians.
The main religious wars on there are French Wars of Religion & the Crusades which total 7 million. I suspect if we include smaller European wars between different churches it would bump up a bit but still most of the killing according to that list did not involve religion as the driving force.
WW1, WW2 was about empire building and in both cases we had a mix of religions on both sides.
WW1 - Muslims+Christians+Hindus+Sikhs (and Japan - not sure the name of their main religion) Vs Christians
WW2 - same except with Atheist Soviets on the side of the Allies and the Japanese with the Nazis.
Then we have the Mongol conquests - mostly non-religious. Different parts of the Mongal empire and their armies had different religions. For example the Blue Horde was headed by a Muslim while other elites where Christians and others had their native Mongol beliefs.
That remaining "large" death tolls are down to Chinese infighting.
Most of the killing is definitely not done in Gods name - ie to promote or spread religion XYZ.