71 Americans have been arrested, indicted, or convicted for their efforts to join or support the Islamic State, known as ISIS, ISIL, or Daesh. 56 of those individuals were arrested in 2015, the most terrorism arrests made in a single year since 9/11.

The U.S. intelligence community estimates that 250 Americans have sought to travel to the Islamic States, with 20 already killed in action.

In October, the director of the FBI reported that the Bureau is pursuing 900 active investigations against homegrown violent extremists, the majority of which are linked to ISIS.

To understand the nature of this growing threat, there is no better place to start than a recent report from the George Washington University Program on Extremism entitled ISIS in America.

The Program’s report documents the diverse social, cultural and religious backgrounds of the Americans involved with ISIS. For instance, Christopher Cornell of Ohio was unemployed and living with his parents two years after graduating from high school. He converted to Islam and planned to set off a series of pipe bombs at the U.S. Capitol. In Mississippi, 22-year-old Mohammad Dakhlalla had enrolled in a graduate program at state university, where his 19-year-old wife Jaelyn Young was a chemistry major. Dakhlalla was the son of a local imam, whereas Young was the daughter of a police officer. The FBI arrested the couple at a local airport as they began their journey to join the Islamic State in Syria, where Young hoped “to raise little Dawlah [Islamic State] cubs.”

The cases of Cornell, Dakhlalla, and Young shows that ISIS recruits may be recent converts or well-informed Muslims; academically successful or struggling to find work; single or married; male or female. Yet all three were young, had no record of extremist activities, and were born in the United States. The activity of the Americans linked to ISIS has spread across 21 states, illustrating the breadth of the threat. Social media played an important role in the radicalization of Cornel, Dakhlalla, and Young, yet personal ties are often crucial.

Regarding the motivations that lead to radicalization, the report from the Program on Extremism observes, “ideological motivations are deeply intertwined with, and impossible to separate from, personal motives.” The Americans who have planned attacks or sought to join the Islamic State abroad see themselves as acting out of a profound sense of obligation to their Islamic principles. Yet this cannot be separated from the “search for belonging, meaning, and/or identity” that they say is so important for both Americans and other Westerns who embrace extremism.

Sometimes, the desperation of this search for meaning becomes painfully apparent. Ariel Bradley of Chattanooga, Tennessee now lives in ISIS controlled territory with her husband, an Iraqi, and their young child. On Twitter and Instagram, Bradley praises the Islamic State to the best of her abilities. An American friend of hers told a reporter, “When I first met [Ariel], she was a Christian, and then she was a socialist, and then she was an atheist, and then a Muslim. As far as I could tell, it was always in relation to whatever guy she was interested in.”

Media coverage of the Americans who support ISIS tends to focus heavily on the role of Twitter, Instagram, Facebook, and other social media applications where the individuals are active. This online environment can often serve as a critical source of information and affirmation for those beginning to turn in a radical direction. It can also provide practical information and connections for those determined to act on their extremist beliefs. The report provides several examples of “individuals whose radicalization was confined to the virtual space, completely devoid of contact with like-minded individuals in the physical world.” In one striking case discovered by the New York Times, an Islamic State supporter located in the U.K. spent hours each day grooming a young woman in rural Washington state. She is active online but has not yet displayed an inclination toward violence.

In many other cases, however, the role of the internet is only “complementary to equally, if not more important dynamics in the physical world.” Often, a small cluster of individuals help to motivate each other and plan illegal activities, while drawing additional support online. Such clusters have been discovered in Minnesota, St. Louis, and the New York metro area.

According to the Program’s report, there is “no silver bullet that will blunt ISIS’s allure” because “there is no standard recruit profile.” The FBI and other law enforcement agencies have made essential contributions to addressing the threat. However, the U.S. government has made little progress in developing programs that prevent radicalization or help to de-radicalize individuals who have broken no laws despite embracing the Islamic State. Furthermore such programs are “woefully inadequate for the task at hand.”

In a separate report published last June, the Program on Extremism evaluated the current state of preventive programs while making specific recommendations for how to improve them. One vital recommendation is the need for coordination across local, state, and Federal governments. Whereas state and local governments must play a key role in implementation, only strong Federal guidance can ensure consistency. While there is much work to be done, there is good reason to hope for bipartisan cooperation on this key issue, since there is now a common sense of urgency regarding the threat of homegrown terrorism.

David Adesnik is the Policy Director at the Foreign Policy Initiative, where he focuses on defense and strategy issues. This article was first published on the FPI’s website.