It is hard to determine how many people are fighting for ISIS or other terrorist groups fighting in this area. There have been several estimates that have been reported, but these are only guesses since a census has never been done. Due to the casualties with the bombings and attacks going on, the numbers may change drastically. Also, recruitments occur with the leaders of ISIS targeting people online with promises of a better afterlife. Recently, it is believed that ISIS has lost many members due to casualties of war.
However, people want to fight for ISIS because they are lonely and are promised a better life where they will belong to a powerful group. Then they join and realize that it isn’t what they thought it would be.