Hello,
After the world war II middle east became a zone of rivalization between Western World and the Soviet Union. For the states of the Middle East it was a great opportunity, because they could choose which one ,,patron'' they want, basing on the offerings of the Soviet Union or the USA.
Both of the Global Powers needed the middle east for their own geopolitical strategy. After the end of the cold war, there was a big vacuum in the middle east, because only America was the one who could give some benefits. Thats why a lot of non govermental jihadist group could gather a lot of people to fight against the biggest enemy - America.
The second alternative to USA was to build own strategical supplies, make own alliances between the states of Middle East. Generally speaking the alliances were fristly grouped in ,,American and non-American'', then both of these groups were divided to Sunni or Shia.
Lack of democratic experiences and religious fundamentalism created a lot of autocratic dictators. The 9/11 caused Arabic Spring where these dictators got overthrown.
Everybody thought that now the societes of Middle East should, or not, they MUST create a liberal democratic system. But there were a big problem. Lack of any group, who had enough power to obtain the legitimation of the society, then change the religion based fundamentalistic system into liberal democratic system, caused that every group who even imitated liberal democratic feelings started to make its own autocratic system. But the status quo ante before the Arabic Spring did not came back, because the power and goods were divided between small groups who were fighting all together.
Western Civilization made a big mistake, because of these steps. Today, it is necessary for USA and Europe to be envolved in this process, but in a new role. The Western Civilization need to figure out how to adapt the liberal democratic values in the society, there is a big problem because the bigger part of society of Middle East is not educated enough in social and politcal sciences to be able to percieve the benefits from liberal democratic system.
Getting into your question, after a short story, which I needed to wrote because my thought are based on the mentioned above history.
If the West withdraw totally from the Middle East, then there will be a huge infringement in regional orderliness, Izreal will be in big problem, because the Arabic world still do not accept the existence of this state. Saudi Arabia can be involved in a huge regional conflict against Iran and other Shia states. There is a huge possibility of humanitarian catastrophies, like using biological weapon.
For Europe that would be a very big catastrophy, the European Union today have a big problem with immigrants, after a big regional war in Middle East, the number of immigrants can be few times more. This can provide more problem among European Union, a lot of right-handed parties and populists parties could be more benefitial on electorat, that can cause that European Union in long run, can fall. Because the distribution of immigrants is a huge problem, because the state parliaments will say no, then the countries who have the most of the immigrants can quit the EU or make a decision to integrate among a close group of states, like western europa states.
The oil prices is also very important, because of a regional conflict, the supplies of oil can be lower, that cause that the oil prices will be very high, or in the second case, the arabic states will try to sell out as many oil as they can. That means the oil prices would go down, even lower than today, that could cause and economic crisis or huge problems among states which economies basing on oil price.
I am very sorry for my bad english vocabulary and grammar, I am trying to improve it day to day, also by posting replies in this forums. Please do not comment my bad grammar or vocabulary, because I am aware of this problem. Please comment on meritum.