I disagree. You can kill a lot of people sure, but there are more to come. And they carry the ideology forward. Sometimes it is in abeyance for a long time, but it does not go away.
By the way, the Mongols who piled up those skulls were Muslims. ISIS is basically following what Tamerlane did in the 1300’s ... using massive violence and force to create a vast caliphate or Islamic empire. That’s 700 years at least that this ideology has been on the rampage. So it’s not that easy to stamp out.
In the meantime, their numbers are growing exponentially and ours are shrinking.
If you are correct, then you have nothing to worry about, as they can’t kill off our ideology either.
I happen to disagree. Extermination works.
Mongols didn’t practice any one religion.