(CNN) On the morning of Donald Trump's inauguration, Keval Bhatt hunted through a closet in his parents' Virginia home for the darkest clothes he could find.

The 19-year-old didn't own much in black, the color he knew his fellow protesters would wear head to toe on the streets of Washington that day.

As Bhatt drove into the city for his first-ever protest, he hesitated.

"I thought, there's a very good chance that I might get arrested, that my whole life could be radically altered in a negative way if I kept driving, and I was really close to turning around," Bhatt told CNN. "But I think the rationale is that even if it did negatively affect my life, I had still contributed to this movement that was necessary. I was still making an effort to make other people's lives better, even if it made my life worse, and once I realized that, I had no regrets."

Bhatt joined protesters dressed completely in black, some with their faces covered by masks -- a tactic known as "black bloc" that aims to unify demonstrators' efforts and hide their identities.

And with them, Bhatt got arrested.

He was rounded up with more than 200 other people and charged with a felony for inciting a riot. He has said he didn't engage in any violence and has pleaded not guilty. A federal indictment charges individuals in the group with starting fires, property destruction and physical violence that erupted on the streets as the 45th President of the United States took his oath of office.

Many of those arrested identified themselves as part of the Antifa movement . Its name derives from "anti-fascist," and it has come to represent what experts who track these organizations call the "hard left" -- an ideology that runs afield of the Democratic Party platform and supports oppressed populations as it protests the amassing of wealth by corporations and elites.

Antifa activists, who operate without any centralized leadership, told CNN that their goal is peace and inclusivity. They often denounce capitalism and government. Since Trump entered the world stage, they've condemned his push to tighten immigration rules and what some view as his tendency toward racism.

While Antifa members don't fit a single category, they say many are millennials and many live on society's fringes: undocumented immigrants, transgender people, low-wage workers, those who don't conform to the traditional 9-to-5.

And their methods are often violent. Antifa leaders admit they're willing to physically attack anyone who employs violence against them or who condones racism -- as long as force is used in the name of eradicating hatred.

From Oregon to Germany

Anti-fascists and the black bloc tactic originated in Nazi Germany and resurfaced in United Kingdom in the 1980s. Large numbers of Antifa activists first appeared in the United States at anti-World Trade Organization protests in 1999 in Seattle , and then more recently during the Occupy Wall Street movement

But their profile has been rising.

Antifa demonstrators have marched in more than a half dozen protests since Election Day in Portland, Oregon, according to police.

Earlier this year, Antifa activists were among those who smashed windows and set fires during protests at the University of California, Berkeley, leading to the cancellation of far-right provocateur Milo Yiannopoulos and withdrawal of Ann Coulter as speakers.

Antifa activists were in New York City on May Day

When the son of Sen. Tim Kaine, the 2016 Democratic nominee for vice president, was arrested in Minnesota in March after protesting at a pro-Trump rally, he was dressed in black bloc alongside a group of Antifa supporters. He faces misdemeanor charges and has not yet entered a plea but will be in court next month. A Kaine spokesperson said he was peacefully protesting, and wasn't disruptive.

And white nationalists, neo-Nazis and others -- who have been blamed for provoking violence at last week's "Unite the Right" rally in Charlottesville, Virginia -- claim it was Antifa groups that first got aggressive. A 20-year-old man who had attended the rally later used his car to ram a crowd of counterprotesters, killing one of them

Indeed, over the past year, Antifa members have been involved in clashes across the country and the world, including in Chicago, Philadelphia, Houston, Alabama and Nebraska, and at the G20 summit in Hamburg, Germany.

"Anti-racists or anti-fascists are not a new phenomenon," said Brian Levin, director of the Center for the Study of Hate & Extremism at California State University, San Bernardino. "What I think is new is that they're more active both in making themselves prominent at violent rallies and also trying to bridge into the disenfranchised peaceful progressive movement."

Bhatt went in Charlottesville, too, and was just about five feet away from the car that drove through the crowd, killing protester Heather Heyer , he said.

Before that, he said, Antifa protesters were cheering in celebration for having disrupted the neo-Nazi message.

"We were marching down one of the streets, and energy was ecstatic," Bhatt said. "We were marching and chanting and engaged in this huge act of solidarity. There was a moment I was at the front of this huge line of people, and we see this other huge group of people marching down another way, and when the two groups met, it felt like the entire city just erupted in cheers and roars."

Spurred to action by Trump

Antifa is impossible to track. It isn't united through a national organization, and it cloaks itself in anonymity.

In speaking to Antifa leaders across the country, CNN found very few who would take off their masks. Indeed, it took months to track down members willing to share their stories.

Many are like Bhatt, a self-described government skeptic with liberal views who didn't find mainstream politics a good fit for him.

So, he weighed his options.

"Before J20 (January 20, Inauguration Day) happened I was convinced I'd go to NASA or some university to research," Bhatt said.

Police and demonstrators clash in downtown Washington, on January 20, 2017, following the inauguration of President Donald Trump.

Now facing a criminal record, "I don't know," he said. "My efforts might be better suited by an organization that helps communities."

The son of parents who immigrated from India, Bhatt is sure of one thing: He has no plans to stop protesting.

"There are people who were energized by Bernie (Sanders) that now are anarchists," said an organizer of the website It's Going Down, a newsblog for Antifa. "People are freaked out by a Trump regime, freaked out by the far-right. A lot of people saw neo-Nazi symbols. There's a reason why people are becoming polarized. It's real-life stuff that's happening."

Sanders, for his part, has disavowed violence and is not connected with Antifa efforts. A self-described democratic socialist, Sanders has come out against "hard-left" violence, saying of protests over Coulter's UC Berkeley appearance, "I don't like this."

"Obviously, Ann Coulter's outrageous -- to my mind, off the wall," Sanders said. "But you know, people have a right to give their two cents' worth, give a speech, without fear of violence and intimidation."

The organizer of It's Going Down said his website traffic has grown from a few hundred daily hits to between 10,000 and 40,000 hits on its best days.

"There's a crisis among the left," he said. "And they're looking for alternatives outside of party structures. The anarchist movement is one that's working outside structures. ... People are excited about that."

Like many young Antifa members who spoke with CNN, the turning point for Bhatt was when Trump in late 2015 ad-libbed a campaign remark toward a Black Lives Matter protester, saying he "should have been roughed up."

In another moment that has catalyzed Antifa members, Trump in February 2016 told a campaign crowd in Cedar Rapids, Iowa, to "knock the crap out of" protesters holding tomatoes, adding, "I will pay for the legal fees, I promise, I promise."

"There was a normalization of political violence which first started with regard to the Trump rallies," Levin said.

"Indeed, we saw alt-right people manhandling African-American protesters," he said, using a term many white-rights activists use to describe themselves . "Then what happened is these fiery embers crossed the fire line, so now on the far-left they say the best way to resist is violence because they're out-gunned in this new era of President Trump."

'This is self-defense'

For almost three decades, Scott Crow was part of the Antifa movement.

"I fought (against) Nazis. I've had death threats. I've had guns drawn on me. I've drawn guns on fascists. I've been in altercations. I've smoke-bombed places," he said. "I've done a myriad of things to try and stop fascism and its flow over the years."

Activists don black bloc, Crow said, as a means to an end.

"People put on the masks so that we can all become anonymous, right? And then, therefore, we are able to move more freely and do what we need to do, whether it is illegal or not," he said.

And that means avoiding police, whom many Antifa members see as an enemy, as well as skirting the scrutiny Antifa activists often get from alt-right trolls on the Internet. Black bloc, one member told us, also unites the movement.

"Even though it only takes one person to break a window, it doesn't matter because the bloc moves together," said a 26-year-old named Maura, who wouldn't give her last name.

In New York's Union Square on May Day, a masked member of the Antifa group Metropolitan Anarchist Coordinating Council told CNN why he wore black bloc and waved a black flag.

"We cover our face because the Nazis will try to find out who we are. And that is a very bad thing because they harass people," he said. "We're trying to stop them from organizing. ... When they organize, they kill people, they hurt people, they fight people. And we're the ones who are fighting back."

It's a position taken by many Antifa activists: "This is self-defense."

Antifa activists often don't hesitate to destroy property, which many see as the incarnation of unfair wealth distribution.

"Violence against windows -- there's no such thing as violence against windows," a masked Antifa member in Union Square told CNN. "Windows don't have -- they're not persons. And even when they are persons, the people we fight back against, they are evil. They are the living embodiment, they are the second coming of Hitler."

Crow explained the ideology this way: "Don't confuse legality and morality. Laws are made of governments, not of men," echoing the words of John Adams.

"Each of us breaks the law every day. It's just that we make the conscious choice to do that," he said.

Antifa members also sometimes launch attacks against people who aren't physically attacking them. The movement, Crow said, sees alt-right hate speech as violent, and for that, its activists have opted to meet violence with violence.

Right or wrong, "that's for history to decide," he said.

But Levin argues the violence is giving ammunition to racists -- and is anathema to the Antifa mission.

"It's killing the cause -- it's not hurting it, it's killing it, and it will kill it," Levin said. "We're ceding the moral high ground and ceding the spotlight to where it should be, which is shining the spotlight on the vile."

Levin, who for decades has attended rallies at both extremes to study radical groups, said he put his own body between an Antifa member and a Klan member when Antifa protesters attacked with knives at a February 2016 a rally in Anaheim, California.

"No, it's not OK to punch a Nazi," Levin said. "If white nationalists are sophisticated at anything, it's the ability to try to grasp some kind of moral high ground when they have no other opportunity, and that's provided when they appear to be violently victimized. That's the only moral thread that they can hang their hats on. And we're stupid if we give them that opportunity."

Rubber bullets and pepper spray

Nearly seven months after Trump's election, police in Portland, Oregon, geared up for the 10th protest since Election Day pitting the alt-right and "hard left."

On that day, June 4, police were coming off a violent May Day protest in which they watched Antifa activists run through the business district, destroying storefronts and setting fires.

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Before the June event, "we saw on social media that there was a lot of threats being put back and forth that gave us a lot of concern about physical violence," Portland police spokesman Pete Simpson said.

Hoping to keep June 4 from becoming another May Day, police created a human barricade. Officers stood shoulder to shoulder between two city squares -- one filled with alt-right groups, the other with Antifa activists.

After a few hours, it seemed peace had won the day. But then police caught whispers that Antifa members were planning to push past police into the alt-right rally square.

Officers moved in with rubber bullets, pepper spray and smoke bombs. They pushed the masked Antifa activists into a corner and detained them. Many shed their black clothing and left it on the streets as police decided whom to arrest.

"We did seize a large number of weapons or things that could be used as weapons," Simpson said. "Everything from knives to brass knuckles to poles and sticks and bricks and bottles and road flares and chains. One hundred percent, they came geared up to fight if it would be allowed."

Police arrest a demonstrator during a protest on June 4, 2017, in Portland, Oregon.

Despite Portland's liberal reputation, it has a history of clashes between extreme groups on the right and left. Residents have gotten fed up with the escalating violence, Simpson said.

"It is new, and this, like, this rumble mentality of, 'I'm going to bring my friends, you're going bring your friends, and we're going to fight it out in the park' -- it's not something we've seen here," Simpson said. "It's not good for the city. People are just frustrated by it. It's affecting their livability. It's affecting their business. It's affecting their commute."

Law enforcement in several cities told CNN there's no excuse for the violence.

"The fires starting -- that we saw on May Day -- is something we haven't really seen much of in the past," Simpson said. "The running through the street, breaking windows and everything in sight, we haven't seen it as consistently as we've seen it in the last eight months."

In that time, more than 150 people have been arrested. They range in age from 14 to 66, police records show, and include several students, a cook, a franchise restaurant owner and a retail manager, a CNN review of arrestees' social media accounts found.

On social media, many of the arrestees have posted anti-police messages and anarchist views. Some write that they feel disenfranchised in the current political climate, the CNN review found.

In Berkeley, Antifa and alt-right activists have clashed several times since Election Day. Police say they haven't seen anything like this since the '60s.

And in jurisdictions across the country, police told CNN they've started enforcing with new vigor laws that bar people from wearing masks during gatherings. For that reason, many Antifa members in Charlottesville did not wear masks, Bhatt said.

"It feels to me like there's a struggle in the country ... of the different kinds of speech and what's OK to say and what's not OK," Simpson said. "But one thing is very clear is that free speech and protected speech can be very offensive and very hateful, but it's still not a crime."

'Put your body in the way'

With no central leader, Antifa adherents have found each other in local communities. They communicate and recruit largely through social media. Their protests are organized via Facebook.

And of late, in active areas, monthly meetings have increased in frequency to several times each week. Activists take martial arts classes together and strategize about how to achieve their main goal: taking down fascists.

Anti-fascist demonstrators confront pro-Trump demonstrators during a protest on June 4, 2017, in Portland, Oregon.

In Portland, where the Rose City Antifa has been active for a decade, members focus on outing people they believe are neo-Nazis, even trying to get them fired and evicted from their homes.

"We've done mass mailings. We've even gone door to door before in communities," said the group's leader, who spoke on condition of anonymity. "We've gone out to areas that we know that a lot of Nazis live with, like, 'wanted' posters, like, 'Do you have any information on this person?' and put them up in the area, and we usually get a flurry of tips like, 'Yeah, this person works here,' and so on and so on."

But like other Antifa groups across the country, the Portland sect gets the most attention when violence explodes at its rallies.

And for that, its members don't apologize.

"You have to put your body in the way," the group's leader said, "and you have to make it speak in the language that they understand. And sometimes that is violence."

It's a perspective several Antifa activists shared with CNN, even knowing that violence has led to hundreds of arrests across the country.

Editor's note: This story has been updated to clarify that counterprotesters say they are not to blame for violence at the Charlottesville protest. The story's headline has also been updated.