WASHINGTON – Islamic extremists have tried to attack America nearly 100 times since the Sept. 11, 2001, atrocities, according to metadata maintained by the Heritage Foundation.

While the vast majority of the attacks were foiled by authorities, 15 over the last six years were successful.

"The U.S. must remain vigilant to the threat of Islamist terrorism," contends David Inserra, a homeland security policy analyst for the Heritage Foundation.

"With the decline of ISIS in Syria and Iraq, the number of terrorist plots in the U.S. have fallen substantially," he wrote. "In 2015, the U.S. faced 17 Islamist plots and attacks; in 2016, 13. So far in 2017, the U.S. has faced only three.

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"It should go without saying that what happens outside America's borders does not necessarily stay there. The violent ideology of Islamist terrorist groups drives many to fight for their cause, especially when these groups appear to be having success or when they are allowed to plot and plan from the safety of a chaotic region."

Inserra explained Sunday at a conference hosted by Heritage that the threat of terror has become more prominent since Sept. 11, 2001, because ISIS has become more prominent, even though al-Qaida has been broken up.

"The variable explaining this is ISIS," Inserra said, noting the uptick in attacks in recent years. "Something changed, ISIS occurred."

It's been 16 years since al-Qaida's horrific attack on the World Trade Center and the Pentagon, but the United States has still not devised an effective strategy to defeat Islamic terrorism, Mary R. Habeck, an adjunct professor of strategic studies at John Hopkins School of Advanced International Studies, said at Sunday's event.

Major problems in defeating Islamic jihadists have included defining the enemy, defining a combat strategy, defining the relationship between the enemy and Islam, citing an objective in war and explaining what victory will look like.

"Looking around the world, what country can honestly say they have defeated Islamist terrorism? The answer is none of them," Habeck said.

In "Stop the Islamization of America: A Practical Guide to the Resistance," renowned activist Pamela Geller provides the answer, offering proven, practical guidance on how freedom lovers can stop jihadist initiatives in local communities.