In an interview with the Atlantic published on Sunday, the former secretary of state says the "failure" of the United States to help those protesting the regime of Syrian President Bashar Assad led to the rise of al-Qaida-inspired groups like ISIL, the militants currently creating havoc in Syria and Iraq.

“The failure to help build up a credible fighting force of the people who were the originators of the protests against Assad — there were Islamists, there were secularists, there was everything in the middle — that failure left a big vacuum, which the jihadists have now filled,” Clinton said.

The former first lady and U.S. senator said she fears the jihadist groups currently gaining strength in the Middle East will expand their sights to Europe and the U.S.

“One of the reasons why I worry about what’s happening in the Middle East right now is because of the breakout capacity of jihadist groups that can affect Europe, can affect the United States,” she continued. “Jihadist groups are governing territory. They will never stay there, though. They are driven to expand. Their raison d’etre is to be against the West, against the Crusaders, against the fill-in-the-blank — and we all fit into one of these categories. How do we try to contain that? I’m thinking a lot about containment, deterrence and defeat.”

Commenting on another Middle East conflict — the war in Gaza between Hamas and Israel — Clinton strongly defended Israel.

“I think Israel did what it had to do to respond to the rockets,” Clinton said. “Israel has a right to defend itself. The steps Hamas has taken to embed rockets and command-and-control facilities and tunnel entrances in civilian areas, this makes a response by Israel difficult.”

She called the deaths of civilians, including Palestinian children, "dreadful," but said, "Ultimately the responsibility rests with Hamas."

“It’s impossible to know what happens in the fog of war," Clinton said. "Some reports say, maybe it wasn’t the exact U.N. school that was bombed, but it was the annex to the school next door where they were firing the rockets. And I do think oftentimes that the anguish you are privy to because of the coverage, and the women and the children and all the rest of that, makes it very difficult to sort through to get to the truth.

“There’s no doubt in my mind that Hamas initiated this conflict," she added. "So the ultimate responsibility has to rest on Hamas and the decisions it made.”

Clinton was asked about President Obama's recently coined slogan (“Don’t do stupid s—-") to describe his administration's foreign policy doctrine.

“Great nations need organizing principles," Clinton replied, "and ‘Don’t do stupid stuff’ is not an organizing principle.”