What made them act that way 100 years ago then? What caused pogroms against Jews throughout the ages? And why do you think that now, unlike then, there is an explanation for it? What makes you think modern antisemitism is different from older antisemitism?
Antisemites act antisemitically because they're antisemitic. It really is that simple.
You're doing Jews all over the world a disservice by trying to justify antisemitic acts.
As mentioned previously, my family left Iraq due to antisemitism before the modern state of Israel even existed. They were chased out. Some were murdered. At no point have I ever thought that the sensible response to this would be to go out and kill / harm / terrorise Iraqis. I also haven't tried seeking revenge on Germans for killing off one whole side of my family except for my grandma.
My husband's family likewise, although they were chased out of Iraq more recently after their friends and relatives were hanged to death in the town square for the crime of being Jewish. At no point have they sought revenge on anyone. They were forced to give up all their land, all their belongings and then fled to Iran who helped give them safe passage to Israel. I know, very ironic. They then moved to the UK. Most of these relatives who safely made it out of Iraq can very clearly see the writing on the wall (sometimes quite literally thanks to prevalent antisemitic graffiti) and are getting increasingly anxious. They know their children and grandchildren are going to suffer similar fates to theirs, despite their best efforts at keeping us all safe.
Antisemites don't need an excuse to be antisemitic, and they really don't need more help explaining their actions. They have already recruited millions upon millions of useful idiots who are willing to defend their actions no matter what. There are more useful idiots doing the antisemites jobs for them than there are Jews in the world. Which is utterly depressing.