ISIS was actually there, founded by Zarqawi like any other group, but its main differentiator was its swift rise to power and popularity after 2011 benefiting from the unbearable oppression of Sunnis in Iraq by Iran and its proxy, which made them align with whoever could be their savior and get rid of the Iranian influence. You can see this clearly when ISIS stormed the prisons where thousands of Sunnis were sentenced to death, and made them into the second wave of recruits.
US did enable ISIS, Zarqawi and co created it, Iran gave people a reason to join it in mass, and international agenda, most importantly the US object to get its enemies (Iran and ISIS) bleed each other, and the Kurdish leftists to ask for its help to the degree to become its proxies, left a space for it to be the monster it was.
Can't also ignore the Turkish and Kurdistani indifference (before ISIS started attacking them, there were ISIS/Kurdistani checkpoints side by side drinking tea together), and the Syrian allowance of fighters flood to Iraq through its the eastern borders since the invasion.
Blaming only the US (although it's the initial culprit) doesn't address the complexity of this problem.