Abu Musab al-Zarqawi started the ISIS group in 1999. During their time together which changed in 2006 during the Iraq War, ISIS gained strength by attacking smaller cities and then taking them over. ISIS was able to know the land since they lived there and through force, they would terrorize the citizens in Syria, Afghanistan and the surrounding countries in the Middle East. As the years wore on, the citizens and government were struggling with the war as ISIS gained its power.
One way that ISIS as able to gain land in Iraq and Syria is through gaining more soldiers and supporters. They would get on the Internet and recruit people by promising them many things. They would target people who were looking for a place where they would belong.