Much has been written about the role of Baathists within the Islamic State. Many of the group’s top commanders are former regime members. A chart made by Truls Hallberg Tonnessen for an August 2015 article in Perspectives On Terrorism labeled “Top leadership of IS 2010-2015 had eight of the thirteen figures being members of Saddam’s government. Joining the organization’s predecessor, Abu Musab al-Zarqawi’s Al Qaeda in Iraq was not so easy as journalist Michael Ware informed PBS’ Frontline back in 2006.
I had another contact with a Baathist commander, mid-ranking, who … was drifting closer and closer towards the Zarqawi organization’s sphere of operation. Essentially he was being recruited. … He in essence said to me, “I have completely rethought that whole strategy.” He said, “I finally sat down with some of the upper echelon” – and this is a man who himself had been in battle since the beginning of the occupation; this is a man who’s killed goodness knows how many American soldiers and Iraqi soldiers – and he said: “I was scared sitting with these men. From one moment to the next, you don’t know what’s going through their minds. And these guys, if they even think you are betraying them, you’re dead.” And he said, “It’s as though they are from another planet.” Then he said to me: “I realized midway through all of this that there [are] only two ways to leave their organization: You either die in battle or you die at their hands.” So he extricated himself and his entire organization from that.
Ware went on to talk about another Saddam era soldier who had joined Zarqawi’s ranks so the two groups were working together, but Ware implied there had to be a real commitment to the group in order to join.
PBS Frontline, “Interview Michael Ware,” The Insurgency, 2/21/06
Tonnessen, Truls Hallberg, “Heirs of Zarqawi or Saddam? The relationship between al-Qaeda in Iraq and the Islamic State,” Perspectives On Terrorism, August 2015