“Your brother created ISIS,” college student Ivy Ziedrich told a startled Jeb Bush after a town hall meeting in Reno, Nevada, in May 2015. The then-Republican presidential hopeful tried to defend his elder sibling, former President George W. Bush, by blaming the rise of the Islamic State on Barack Obama, “because Americans pulled back” from Iraq in 2011.

It sounds a bit conspiratorial, right? Calling Dubya the creator of ISIS? The reality, however, is that Ziedrich’s accusation wasn’t far off the mark.

Had it not been for Bush’s catastrophic decision to invade and occupy Iraq in 2003, in defiance of international law, the world’s most feared terrorist group would not exist today. ISIS is blowback.

In this week’s episode of my six-part series on blowback, I examine the three ways in which Bush’s misadventure in Mesopotamia helped birth a group that the U.S. now considers to be one of the biggest threats to both U.S. national security and Middle East peace.

First, foreign military occupations tend to radicalize local populations and breed violent insurgencies. Take Hezbollah in southern Lebanon. Or Hamas in the Gaza Strip.

In Iraq, the U.S. morphed from heroic liberators into brutal occupiers within a matter of weeks. In Fallujah, which would later become an ISIS stronghold, U.S. troops opened fire on a crowd of peaceful protesters in April 2003, killing and wounding dozens of Iraqis.

The shootings, the torture, the general chaos, all helped drive thousands of Iraqis from the minority Sunni community into the arms of radical groups led by brutal gangsters, such as Abu Musab al-Zarqawi. Zarqawi’s Al Qaeda in Iraq, formed in 2004 to fight U.S. troops and their local allies, was a precursor organization to … ISIS.

Second, in May 2003, in a criminally stupid and reckless move, the U.S. occupying authorities disbanded the Iraqi army. That’s right: The U.S. made more than half a million well-armed and well-trained Iraqi troops unemployed overnight. No less an authority than Gen. Colin Powell, Bush’s secretary of state and America’s former top soldier, would later describe those jobless soldiers as “prime recruits for insurgency.”

In recent years, many of the top commanders in ISIS have been identified as former senior officers in Saddam Hussein’s army. Coincidence?

Third, the U.S. military detained tens of thousands of Iraqis, many of them noncombatants, at Camp Bucca in southern Iraq, where imprisoned jihadis were able to not only radicalize new recruits in plain sight, but also plan future operations and attacks. “Many of us at Camp Bucca were concerned that instead of just holding detainees, we had created a pressure cooker for extremism,” compound Cmdr. James Skylar Gerrond would later remark.

One former Bucca detainee, incidentally, was none other than Abu Bakr al-Baghdadi. Yes, the self-proclaimed caliph and leader of ISIS who, according to Iraqi terrorism expert Hisham al-Hashimi, “absorbed the jihadist ideology and established himself among the big names” while at Bucca.

To be clear, then, ISIS is blowback from the U.S. invasion and occupation of Iraq. And don’t just take my word for it. Listen to David Kilcullen, a former adviser to both Gen. David Petraeus and former Secretary of State Condoleezza Rice, considered to be one of the world’s leading counter-insurgency experts. “We have to recognize that a lot of the problem is of our own making,” Kilcullen told Channel 4 News in March 2016. “There, undeniably, would be no ISIS if we hadn’t invaded Iraq.”