The jihadist movement is a global insurgency – not just a terrorist phenomenon. Today, most of the world's jihadist groups have affiliated themselves with one of two poles: al Qaeda or the Islamic State. This seeming unity, however, belies numerous disagreements about how to pursue jihad. Much of this fractiousness stems from the many mergers of earlier extremist groups who have brought their own histories and philosophies into the new larger groups of al Qaeda and the Islamic State. This contentiousness is perhaps most vividly illustrated by the relationship between al Qaeda and Jamaat al-Tawhid and Jihad, the group led by Abu Musab al-Zarqawi that joined the al Qaeda movement in 2004 – only to split from it in 2014 to form the Islamic State, creating a competing pole in the jihadist movement.