What are the main causes (underpinnings) of terrorism?

There are several factors that can lead to acts of terror. The causes of terrorism can be broken down into three categories, which are political, socioeconomic, and religious.
Socioeconomic factors can lead to terrorism because people may feel they have no hope or escape from the conditions of poverty in which they live. They may be promised a significant amount of money to carry out terroristic acts. These people also may have had limited educational opportunities, which have prevented them from advancing economically and from fully understanding the causes of their unhappiness. They hope that their actions will lead to an improved life for themselves and for their people.
Political factors often lead to acts of terrorism. When people feel they have been politically wronged, they may feel the only way to make their point is to strike in violent ways. Some of the acts of terror that have occurred recently can be traced to groups who feel the Western world has exploited various groups of people. These people feel the West got wealthy at the expense of groups of people living in different parts of the world. They are lashing out at Western ways of living, which they view as greedy and centered on only improving Western society and standards of living. In other instances, people feel they have been denied land and strike violently in order to gain the land that they feel they should have.
Religious beliefs also contribute to terrorism. Much of the terrorism in the world today can be traced to Islamic groups that believe they are acting in the name of G—d. They feel they will be viewed as martyrs by carrying out these acts of terror and will be rewarded in the afterlife for their actions.
http://handofreason.com/2011/featured/causes-of-terrorism

https://www.thoughtco.com/the-causes-of-terrorism-3209053