Because the people who created Christianity had created it to replace Judaism and tried to wipe out all the Jews. And they kept trying to do this throughout history. It was the Catholic Church specifically, from the earliest time of its creation, which tried and tried to get rid of as many Jews as possible - and they tried many different ways of doing it.
One thing that you should look into regarding this is just what all three "reich" really were. The Third Reich, for instance, most people do not know was another name for the continuance of the Holy Roman Empire, of which, the Catholic Church was the head of. So, contrary to what you may have heard of regarding the Catholic Church during Hitler's reign, it had a vested interest in the final solution.
And no doubt was secretly helping Hitler. BTW, the crusades too, were not simply about regaining the holy land. They were an excuse to send hoards of hate filled loyal believers through Jewish towns and villages along the route so that they could destroy and plunder those villages as well, and return with the plundered loot as offerings to the Church.
And then there were the Inquisitions... It is ridiculous to say that the Catholic Church has not always tried to destroy the Jews. The Jews of the first century tried to prevent the psychopaths creating Christianity from doing the deed in the first place. That is why.
Consider what Og, the king of the giants heard from his scout.."Well sire,,it appears that the Hebrew slaves have been freed from Egypt..They have been observed marching in formation through the wilderness,,and they seem to be following a gigantic pillar of fire by night and a pillar of smoke in the daytime" Everybody hates the rich kid and the winner. THe Jews have been proclaimed to be God's chosen people. Your point is well founded since Jesus is a Jew and did not come to start anew religion, but to put the finishing touches on the covenant with Isreal.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.