I know how to decrease terrorism in the world. Terrorism starts in the mind as a seed. The seed grows from anger. A man or woman that is always filled with anger looks for something to channel their anger into and they find things on the internet or in their imagination.
They key is to remove the angry seed before it can grow. I would regulate media more so there is less Anger and violence. I would also change the street lights so they are pink and blue. Some of the street lights are pink and the others are blue. Pink and blue light are good for the mind.
I would put speakers inside street posts like lamp posts and street signs that emit the sound of a monk chanting because the sound of a monk chanting turns off angry thoughts, "ommmm, ommmmm" like that.
I would make the litigation system simpler. Complexity makes people angry. People like simple things.
There are many other things I would do but I don't have time to talk about them.