Wars do not have single causes. Finding among the causes or motivations of leaders secular or temporal goals does not mean religion did not play a major role in a war, both as a justification and as a motivation for those fighting them.
The Crusades were explicitly religious, yes there were other motivations, the Roman emperor wanted to regain some territory, various lords sought new lands in the Levant. But for most fighting the early Crusades, it was religious.
The sack of Constantinople is another that had many causes, but among them was vengeance for the "Massacre of the Latins" which again had many components but among them was the widening religious differences between the Patriarch and Pope.
But all of that is the usual tit for tat blah blah blah. The real issue here is religion and WW2. While its complex, resources were definitely a\the major motivation but the war was justified and motivated as a war against "Judeo Bolshevism".
Field-Marshal Wilhelm Keitel gave an order on 12 September 1941 which declared: "the struggle against Bolshevism demands ruthless and energetic, rigorous action above all against the Jews, the main carriers of Bolshevism".
Historian Richard J. Evans wrote that Wehrmacht officers regarded the Russians as "sub-human", and were from the time of the invasion of Poland in 1939 telling their troops the war was caused by "Jewish vermin", explaining to the troops that the war against the Soviet Union was a war to wipe out what were variously described as "Jewish Bolshevik subhumans", the "Mongol hordes", the "Asiatic flood" and the "red beast", language clearly intended to produce war crimes by reducing the enemy to something less than human.
Joseph Goebbels published an article in 1942 called "the so-called Russian soul" in which he claimed that Bolshevism was exploiting the Slavs and that the battle of the Soviet Union determined whether Europe would become under complete control by international Jewry.
Nazi propaganda presented Barbarossa as an ideological-racial war between German Nazism and "Judeo-Bolshevism", dehumanising the Soviet enemy as a force of Slavic Untermensch (sub-humans) and "Asiatic" savages engaging in "barbaric Asiatic fighting methods" commanded by evil Jewish commissars whom German troops were to grant no mercy. The vast majority of the Wehrmacht officers and soldiers tended to regard the war in Nazi terms, seeing their Soviet opponents as sub-human.
As with all complex events "there is more too it than that". Normally let it pass. But 6 million people were murdered because of their religion, it was widely cited as a cause for the war by the country initiating it. From a UK perspective it was mostly a war about stopping Hitler. We dont really think of it as religious. But from inside the Third Reich, religious bigotry was a keystone of the regime and its long term goals.
Also WWI had a religious angle to it that still resonates today: the Ottoman Sultan, Mehmed V, called the Umma to Jihad (14 November 1914). Outside of the Ottoman Empire most of them ignored him. But again this led indirectly to the Armenian Genocide. Armenians were Christians. Turkish xenophobia (ironically for people who had been in Anatolia far longer than them) also played a major role, again.... complex.
Religion has played a critical role in our history. Good, bad and utterly fucking horrific.
Dragging it back to a vague relevance of the topic. Perhaps Religious Education should teach children the roles that each religion has played in justifying wars, genocides, slavery and all the other horrors in the dark underbelly of humanity. (Muhammed ibn Abdullah was a slave owner and a slave trader, though I am not sure this will go down well as something for RE class).
And before people start going on about Buddhists, they are currently engage in ethnic cleansing and genocide in Myanmar. (This one against Muslims)
For every single thing I have said someone can say "but this other thing....". Religion has played a role in justifying a large amount of horror and wars.