Colin Powell went to the UN and gave a 20-minute speech about Al-zarqawi, the future founder of ISIS, and claimed he was a link between Al-Qaeda and Saddam Hussein to try to link them together to justify invading Iraq. No one had ever heard of Al-zarqawi before Powell's speech because he was pretty much a common pimp and criminal, but that allowed him to get notoriety and start his caliphate and form ISIS
Like you said they didn't directly form ISIS but they gave the founder the ability to do it.
When you do what you love, you'll never work a day in your life.