Please don't ask for things that can't reasonably exist.

I can't come up with any experiment that could produce and reproduce peer-reviewed research on the causes of terrorism. It would either be horribly unethical, or it would be horribly impractical.

We cannot ask dead terrorists to fill out survey questionnaires on why they decided to commit terrorist attacks. It is extraordinarily difficult to obtain a blinded, representative sample of live terrorists, and nearly impossible to get valid mailing addresses for sending out their questionnaires. Even then, the response rate would be abysmally low. You might be able to interview captured terrorist suspects, but their responses might be biased by the conditions of their captivity. And all that presumes that a terrorist actually knows why they do what they do.

We can't take a group of non-terrorists, apply experimental treatments and the control treatment, and release them into the wild to see if any would then go on to commit a terrorist act. That would be unethical to begin with, and the method of observation would almost certainly influence the results.

So it should be reasonably well established that everyone advancing a potential contributing cause for terrorism is stating yet another hypothesis, none of which can be reasonably tested in the real world. As such, it would be acceptable to employ simulation models, Monte Carlo methods, behavior studies on lesser mammals, and any of several other means, none quite as good as a real-life scientific study using live humans.

So what you should probably be asking for is the computer simulation model that was used to show that immigration fuels terrorism. Then we could productively argue over how flawed and simplistic the model was, and how it should have been written in a different language, or using a different software paradigm. And then someone, inevitably, would ask:

What does any of this have to do with desalinization membranes?!

There's definitely peer-reviewed research on terrorism, but I'm no expert. But yes please, let's stop this discussion now. I'm sorry for going off topic.