Oh come on

Why not turn the other cheek with the Muslims and simply defend Europe rather than invade other lands and put them into our control? The Reconquesta was well under way in Spain. The lands conquered by the Muslims in the Arab Invasions had been in there hands for hundreds of years.
We didn’t have any need, really, and our “help” to Byzantium resulted eventually, long-term, with the horrendous Sack of Constantinople which sounded the death knell for the Empire and is a key cause for its ultimate collapse into Turkish hands. We could I am sure have defended Byzantium without claiming land for ourselves and minus the terrible massacres of civilian Muslim populations such as during the Siege of Constantinople.
Now we cannot impose the Geneva Convention on Middle Age people. What the Christians did was not “awful” or illegal by the standards of the time but in our modern eyes it would constitute war crimes. And that’s the point I am making.
I’m not saying the Crusades
didn’t have a just cause (I actually believe that they did), I am merely presenting you with an alternate understanding. To call the Crusades “holy” (NO WAR IS HOLY or can be since it results in the loss of human life) and to hold them up as an exemplary instance of just combat, without looking at them in historical context, and while likewise trying to undermine the necessity and justice behind World War Two, is way off in my opinion.
You seem to forget that Hitler, aka the Hossbach Memorandum 1937, intended to dominate Eastern Europe to achieve lebensraum and then eventually the entire European continent. Hitler even planned for war with America for the mid 40s.
He fought a war of annihilation in Poland.
Could Hitler’s intention in Poland have been any clearer? Should the world have sat back and let Hitler annihilate peoples he considered to be “inferior races”?
Not to mention his desire to eliminate the Catholic priesthood and hierarchy in Poland. At Leczyca, the Jesuits were expelled from their residence and forced to watch as their church was looted of sacred vessels, vestments, reliquaries and works of art. The priests were not even allowed into the church to save the Blessed Sacrament. Most of the priests were arrested and sent to concentration camps.
In Germany in 1935, Hermann Goering gave the rationale for crushing the Church: “
Catholic believers carry away but one impression from attendance at divine services and that is that the Catholic Church rejects the institutions of the Nationalist State.”
And they were right to suspect Catholics of disloyalty to the Reich. Catholics protested against the removal of crucifixes from Bavarian schools in 1941, during which they tossed out of classrooms and burnt the mandatory pictures of Adolf Hitler, replacing them with the banned crucifix.
Blessed Clemens August Von Galen, the bishop of Münster, spoke out against the Nazis’ euthanasia program during World War II and became the inspirer of the White Rose resistance movement within Germany.
Hitler expected a full-scale European war with Britain and France between 1941-1944/5 and then the USA.
If Britain and France had not declared war on him BEFORE he invaded Russia, he would have been unstoppable
and there would be no Catholic Church today, since Hitler called its clergy “walking abortions in cassocks” and detested the Pope.
And you are trying to suggest that Britain and France should have let Hitler annihilate the Polish people, send all its priests, Bishops, intellectuals etc, to concentration camps and then plough on into Russia and after obtaining that Lebensraum then move on to dominate Europe and then attack the USA?
And please I’m not even going to debate over Japan, since the morality of US action is blindling obvious.
PS I do believe the Crusades had a just cause, although like World War II not all the actions of the Christians were in accordance with just action.