What do this sites of terrorist activities
have in common? Why is there heavier terrorism activity in certain area of the world?
first question: I have no idea what you mean.
second question: the essence of terrorism is to make terror reign amounst a population, by killing, maiming usually the innocent. Terror is always a balance of conscience versus goals. Some cultures have certain goals as ranked very high as desirable (like killing infidels), and very low on conscience (others lives are not worthy). So culture has a lot to do with it. Other factors: selfworth, poverty, religious zeal, sense of belonging to a cause, hatred for others.