(1) Islamic State was founded by the followers of Zarqawi after his death in a US bombing in 2006.
(2) Zarqawi,a Jordanian, went to Afghanistan to fight the Soviets in the 1980s, founded his own terror outfit 'Jund Al Sham' in Jordan in 1992, visited Pakistan in 1999, set up a training camp funded by Osama Bin laden in Afghanistan that year and finally entered Iraq to fight the US-led forces before his death.
(3) The strength of Islamic State militants is estimated to be about 20000-30000 in Syria but Wikipedia puts it at 1,00,000 with another lac in Iraq.
(4) Foreign militants have infiltrated the Islamic State and have alienated the terrorist outfit from other Syrian rebels and the people of Syria at large.
(5) Iran and the Assad Government in Syria protected Zarqawi from foreign governments just like America protected Osama Bin Laden from the Soviets during the Afghan Civil War. In both these cases, the ungrateful terrorists did not just bite off the hands that fed but reached out to vanquish the hearts of these opportunistic world powers. When will these fools ever learn that your enemy's enemy is not necessarily your friend?