What would help would be writings or speeches where the governing elites were using religion as a major justification for their fighting. While they all prayed for victory, this was nothing like the Catholic-Protestant wars of the 1500-1600s. Nor do I recall any evidence of Woodrow Wilson justifying American entry into the war because the Germans were heretics.
I was thinking along these lines. Practically every nation in WWI entered the conflict because of some alliance with another nation, who had an alliance to another nation, and so on and so on.
The two exceptions to this were the US and Japan. Japan saw it as a means of appropriating the German-controlled area of Qingdao in China as part of its own expansionist plans; among other results, the Japanese got control of Tsing Tao beer, which switched to control under Asahi.
The US wanted to stay neutral because we didn't feel like losing our men the way everyone else was losing theirs, and also our industries were producing lots and lots of ordnance and such to both sides. It was only when it looked like Germany was going to promote Mexico's starting another war with us, along with the Lusitania and similar incidents, that we finally got mad enough to enter the war against the German alliance. What happened after that is where the picture changes...
Barbara Tuchman’s Guns of August is one of the better histories of WWI. I read that and one by a British historian, maybe Keegan.
Neither mentioned any religious motive for the war. The leaders of the countries involved were mostly cousins related through Queen Victoria.
The Ottoman Empire was crumbling. Now forgotten Austro-Hungary used the assassination of their Archduke as the reason for a Balkans land grab. This triggered a bunch of alliances to react and all of Europe blundered into a suicidal war. No religious conflict involved.