WASHINGTON >> They were young men caught between cultures, sons of immigrant families, feeling lost or rejected — and angry about American-led wars. Online they encountered the silver-tongued recruiters of al-Qaida and the Islamic State, who said their first loyalty should be not to their nation but to Islam. Then they plotted sensational violence.

In the weekend bombings in New York and New Jersey and stabbings at a mall in Minnesota, the accused perpetrators fit the same rough pattern as in previous attacks at the Boston Marathon in 2013; in San Bernardino, Calif., in 2015, and in Orlando, Fla., in June, as well as in the terrorist assaults in Paris and Brussels.

A rich recruiting pool for al-Qaida and the Islamic State includes what psychologists call “in-betweeners,” young adults whose identities have not yet solidified. Their uncertainty makes them vulnerable, said J. Reid Meloy, a forensic psychologist and clinical professor at the University of California, San Diego. “It allows the individual to attach his identity to something that is larger and inflates his sense of himself,” he said.

The uncomfortable in-between status can be especially acute for those with recent immigrant roots. Living in two cultures at once is very enriching for most people but very unsettling for others, said Lorenzo Vidino, the director of the Program on Extremism at George Washington University.

For some Muslim immigrants, he said, “You have a message at home that’s very conservative, and a completely different message from the society around you when you’re growing up.”

The full history of Ahmad Khan Rahami, 28, the naturalized American of Afghan birth who is accused of planting bombs in Manhattan and New Jersey, is not yet known. But his 2014 arrest in an alleged stabbing in a family dispute suggests a young man adrift; his scribbling in a notebook the names of Osama bin Laden, Abu Muhammad al-Adnani — an Islamic State leader — and Anwar al-Awlaki, the U.S.-born al-Qaida recruiter, appeared to reflect a full-blown embrace of jihadism.

Tamerlan Tsarnaev, a Chechen immigrant and the older of the two Boston Marathon bombers, turned to Islamist extremism when his hopes for a boxing career dimmed. He was 26 at the time of the attack. Omar Mateen, the son of an Afghan immigrant with outspoken political views, was 29 when he opened fire at an Orlando nightclub, killing 49 people. He had been dismissed from training as a prison guard after making disturbing remarks about weapons, and ended up as a private security guard.

Syed Rizwan Farook, 28, the Chicago-born son of immigrants from Pakistan, found work as a health inspector but had spent years searching for dates and a mate before meeting Tashfeen Malik online and marrying her in Saudi Arabia. Together, the couple attacked a luncheon attended by Farook’s colleagues in December, killing 14 people.

“When you dig into these cases, you find the ‘why’ is a very complex question,” said Peter Bergen, the director of the security program at New America, a research group, and author of “United States of Jihad.” Personal disappointment, perceptions of discrimination, anger about U.S. foreign policy and the desire “to become a hero in one’s own story” are all at play in addition to jihadi ideology, he said.

“Many of them just take their grievances and dress them up in the garb of Islam,” Bergen said.

That has become easy in the age of the internet. The attackers in San Bernardino, Orlando and New York all had expressed support for the Islamic State, and they and the Boston bombers were devotees of the voluminous online work of al-Awlaki, who was killed in a U.S. drone strike in 2011. He remains highly popular on the web, where he argues that Western Muslims must reject even the friendliest non-Muslim neighbors, whom he calls “Sally Soccer Mom and Joe Six-Pack.” Rahami wrote in his journal that “Sheikh Anwar,” as well as al-Adnani of the Islamic State, had “said it clearly”: “Attack the kuffar,” or non-Muslims, “in their backyard.”

Farhad Khosrokhavar, a sociologist at the Ecole des Hautes Etudes en Sciences Sociales in Paris and the author of “Radicalization,” said Muslims in Europe more often than those in America felt “frontally rejected” by the larger society. He said he has often seen in his research individuals who felt neither French nor Arab.

“In France, they are blamed for not being French enough, and when they go to their parents’ country of origin, they are blamed for not being Arab enough,” Khosrokhavar said. “That double denial can push them to adhere to a radical version of Islam, as a kind of lifeline: Since I am neither French nor Arab, neither American nor Afghan, I am Muslim and to hell with you all,” he added.

These roots of radicalization do not make immigrants in general a danger. In the United States, immigrants have a lower rate of crime and violence than other Americans. Converts to Islam are disproportionately represented among Americans and Europeans drawn to extremism, and other ideologies also motivate mass violence — as in the case of Dylann Roof, who was 21 when he fatally shot nine black people last year at a church in Charleston, South Carolina, in the name of white supremacy.

“The actual content of the ideology is secondary,” said Meloy, the psychologist. “What’s important is the identification and fixation.”

But the Islamist terrorist groups target the particular anxieties of Western Muslims from immigrant backgrounds, posing recruitment as a religious loyalty test. They call on supporters to reject the nations where they live and embrace instead a devotion to the ummah, the global community of Muslims. The West is at war with Islam, they say, and you must strike out to defend your fellow Muslims.

That message has been delivered with particular power by al-Awlaki, often reinforcing the newer propaganda efforts of the Islamic State. As an imam who counseled immigrants at three American mosques, and as a Yemeni-American who had lived in both countries and in Britain, al-Awlaki understood the worries of Muslims in the West. When he joined al-Qaida, he did his best to open a gulf between them and their non-Muslim neighbors.

“The important lesson to learn here is: Never, ever trust a kuffar,” al-Awlaki said in a 2003 lecture in London that was captured on video and remains a YouTube favorite. “Now, you might argue and say: ‘But my neighbor is such a nice person. My classmates are very nice. My co-workers — they’re just fabulous people, they’re so decent and honest.’” Yet these non-Muslims can never be relied upon, he said.

Later, after moving to Yemen, he spoke not only of shunning non-Muslims, but also of attacking them. In a 2010 video, he tried to shame his listeners into choosing his brand of religion over their country.

“To the Muslims in America I have this to say: How can your conscience allow you to live in peaceful coexistence with a nation that is responsible for the tyranny and crimes committed against your own brothers and sisters?” he said. “How can you have your loyalty to a government that is leading the war against Islam and Muslims?”

He has led many people down the jihadi path, and not just in English-speaking countries. The Counter Extremism Project, an advocacy group based in Washington, said Wednesday that it had counted 88 “extremists” who had been influenced by al-Awlaki: 54 in the United States and 34 in Europe.

Most such jihadi recruits are the children of immigrants, said Olivier Roy, a professor at the European University Institute in Florence, Italy, and the author of “Globalized Islam.” His research shows that 65 percent of Muslim extremists in France and Belgium are from this second generation.

“These young people have broken away from their parents, who they blame for many things — for practicing the wrong Islam, for having brought them to the West, for having failed in life,” Roy said, noting that Rahami reportedly had clashed with his father.

But such conflicts pass. Few jihadis are from the third generation, the grandchildren of immigrants, he said.