A new report demonstrates “unprecedented” “ISIS-related mobilization” in the United States, only weeks after some considered the threat posed by Islamic State to be contained.

The report, “ISIS in America,” released by George Washington University’s Program on Extremism was authored by Lorenzo Vidino and Seamus Hughes. Dr. Vidino, director of the Program, has held positions at the Kennedy School of Government, the U.S. Institute of Peace, the RAND Corporation, and the Center for Security Studies (ETH Zurich).

“ISIS-related mobilization in the United States has been unprecedented,” the report states in its executive summary. While the presence in the U.S. is not as large as many countries, some 250 Americans have traveled or attempted to travel to Syria/Iraq to join the Islamic State and there are 900 active investigations against ISIS sympathizers in all 50 states.

Seventy-one individuals have been charged with ISIS-related activities since March 2014.

Fifty-six have been arrested in 2015 alone, a record number of terrorism-related arrests for any year since 9/11.

The report provides a fascinating profile of ISIS sympathizers in the U.S.: Of those charged, the average age is 26 and 86% are male. Their activities were located in 21 states.

Fifty-one percent traveled or attempted to travel abroad. 27% were involved in plots to carry out attacks on U.S. soil.

The report reveals that individuals involved in ISIS-related activities in the U.S. differ widely in race, age, social class, education, and family background. “Their motivations are equally diverse and defy easy analysis,” the report states.

Social media including Facebook and Twitter plays a crucial role in the radicalization and, at times, mobilization of U.S.-based ISIS sympathizers. The Program on Extremism has identified some 300 American sympathizers active on social media, spreading propaganda, and interacting with like-minded individuals.

“Some members of this online echo chamber eventually make the leap from keyboard warriors to actual militancy,” the report notes.

“American ISIS sympathizers are particularly active on Twitter, where they spasmodically create accounts that often get suspended in a never-ending cat-and-mouse game. Some accounts (the “nodes”) are the generators of primary content, some (the “amplifiers”) just re tweet material, others (the “shout-outs”) promote newly created accounts of suspended users.”

ISIS-related radicalization is not limited to social media. Some cultivated and later strengthened their interest in ISIS through personal relationships. “In most cases online and offline dynamics complement one another.”