And the forces that likely shaped their childhood, Russian experts say, included a bleak landscape of war and destruction, deep poverty, and a Chechen warrior tradition that stresses male independence, individual courage, and defiance of authority.
According to Russian news media, Dzhokhar – who is still on the run – and Tamerlan Tsarnaev left Chechnya as children in 2000, at the height of Russia's bloody second invasion of the independence-seeking republic. Though there are many versions of their story circulating, Russian reports indicate they lived for about a year in the neighboring republic of Dagestan, which has been wracked for more than a decade by a growing Islamist insurgency.
They subsequently moved to Turkey, where Russian media reports say they gained citizenship, before emigrating a few years ago to the US.
But, judging from Dzhokhar's page on the Russian-language social media site VKontakte – possibly updated as recently as 5 a.m. this morning – and YouTube videos posted by Tamerlan, the two brothers retained a close affinity to their Chechen roots.
"Dagestan, where these two boys lived and went to school for some time, was – and is – a deeply criminalized republic where daily conditions can only be described as warfare," says Vadim Kozyulin, an expert with the PIR Center, a leading security think tank in Moscow.
"For young people from these places, it's crucial for their self-respect that you are independent and strong. Most young men practice martial arts of some kind – we know the older brother, Tamerlan, was a boxer, the younger, Dzhokhar, was a wrestler – and this culture facilitates a tendency to quick violence," he says.
A history of war
Russia's volatile, mainly-Muslim northern Caucasus, which includes Chechnya and Dagestan, was conquered by Imperial Russia after a bloody decades-long scorched-earth campaign in the 19th century. Gen. Mikhail Yermolov, who led Russian forces in battle to pacify the Chechens, called them "congenital rebels." Novelist Mikhail Lermontov, who took part in that struggle, was more admiring of the Chechens, writing in 1832: "Their god is freedom; their law is war."
Once subdued, the Chechens revolted repeatedly against Russian rule. In 1944, Soviet dictator Joseph Stalin accused the Chechens of collaborating with the invading Nazis and ordered the entire Chechen population, half a million people, deported to Central Asia and Siberia. An estimated 150,000 died during the forced winter march.
Reformist Soviet leader Nikita Khrushchev allowed the Chechens to return home in 1956, but the embers of revolt continued to simmer. When the Soviet Union collapsed in 1991, Chechnya declared independence under its first leader, former Soviet Air Force Gen. Dzhokhar Dudayev, after whom the younger Tsarnaev is very likely named.
Then Russian President Boris Yeltsin ordered his army to invade the little republic in December 1994, after his defense minister assured him the Chechen insurrection could be defeated by "one division of paratroopers in one afternoon."
Instead, the Russian army was defeated after two years of bitter warfare that killed an estimated 80,000 civilians and left Chechnya in ruins. But in peace, Chechnya broke apart. Powerful Chechen warlords such as Shamil Basayev and the Jordanian-born Emir Khattab turned to Islamist ideology and international organizations like Al Qaeda for assistance.
In 1999, Chechen forces led by Mr. Basayev invaded Dagestan, prompting Russia – now under an untested new prime minister named Vladimir Putin – to invade Chechnya again. After a decade of brutal warfare, accompanied by savage military "cleansing" campaigns in the Chechen countryside, Russia finally declared victory in 2009, pulled its army out, and left the republic under control of a pro-Moscow strongman named Ramzan Kadyrov. Since then, Chechnya has enjoyed a stunning economic rebirth under Mr. Kadyrov's near-totalitarian rule, a fact that causes great pride among the far-flung Chechen diaspora.
'Fertile soil for Islamist recruiters'
Russian experts puzzling over the younger Tsarnaev's VKontakte page Friday say they see few signs that the young man could have been influenced by the strict Salafist Islamist ideology that has penetrated deeply into the war-torn Caucasus over the past 15 years. On the page he describes his worldview as "Islam," but goes on to identify his main personal goals as "career and money." He also posts links to a site with videos glorifying jihadist fighters in Syria, and another that advocates Chechen independence from Russia.
However, YouTube videos posted by his now-deceased older brother included several albums, one of which is called "Terrorist." Also posted were audiotapes by Faiz Mukhammad, a Muslim cleric famous for his radical views, and videos by Chechen singer Timur Mutsuraev, several of whose songs have been banned by Russia's Justice Ministry as "extremist." (Several items have since been deleted from the account.)
"Russia has had enormous troubles with Chechnya. The echoes of those terrible wars are still with us," says Alexei Mukhin, director of the independent Center for Political Information in Moscow.
Chechen terrorists have struck Moscow and other Russian cities repeatedly, including a horrific theater siege that killed 120 in downtown Moscow in 2002; a double suicide bombing in the Moscow metro 3 years ago that killed 40 people; and a suicide bombing in Domodedovo airport the next year that killed 35 people.
"The young people emerging from that crucible have absorbed a culture of violence and hatred. They imagine themselves as warriors, and this makes them very susceptible to the idea of jihad today," says Mr. Mukhin. "Islamist recruiters in the north Caucasus are cultivating very fertile soil.... The idea of the individual act of heroism, that brings glory and renown, is deep in Chechen male culture. When motivated by ideology, it can be a very powerful impulse."
Why the US?
But Chechens have little history of striking outside of the north Caucasus and the heartland of their traditional enemy, Russia. Rumors of Chechen terrorist networks in Afghanistan and the Middle East have often proven false or greatly exaggerated, say experts.
"These young men don't necessarily need to be connected to any wider terrorist network like Al Qaeda," says Andrei Soldatov, a security expert and editor of agentura.ru, on online journal that focuses on the security services.
"It's difficult to understand why Chechens would decide to strike in the US," especially since US foreign policy was supportive of Chechnya's long struggle for independence from Moscow over the past two decades, he says.
"But these days a connection with a wider network is not needed for individuals to become inspired. They can arrive at this decision on their own, and find materials to inspire them on the Internet, through social media. That's what makes it such a daunting challenge for security services," he adds.