Thousands Protest Nationwide for the 'Greater Good of Humanity' Following Police Shootings

— -- Thousands of people took to the streets of cities across the U.S. Friday night -- many against the backdrop of watchful riot gear-wearing police -- following the police shootings of black men in Louisiana and Minnesota, and the deadly sniper attack on police officers in Dallas.

Howard University student George Wyche, who took part in a rally outside the U.S. Department of Justice in Washington, D.C., conveyed a sentiment common among those taking to the streets to seek an end to police violence: "It's a time for belief in the greater good of humanity," he told The Associated Press.

While most of the gatherings nationwide were peaceful, at least 90 people were arrested or detained by law enforcement officials across the country, with pepperballs and stun guns unleashed by riot gear-wearing police in some cities.

The most chaotic demonstrations were those in Phoenix; Baton Rouge, Louisiana; and Rochester, New York.

The scene in Phoenix was dramatic, with riot gear-wearing police unleashing non-lethal pepperballs against protesters at a rally that began outside city hall, organized by civil rights leader Rev. Jarrett Maupin. Despite the seemingly chaotic imagery, only three individuals who threw rocks at officers were arrested.

About 1,000 people chanted "black lives matter" and "hands up, don't shoot" as they marched in downtown Phoenix.

Minor scuffles broke out when a man wearing a "Make America Great Again" T-shirt and holding a Donald Trump campaign sign pushed his way into the protest. Police pulled the man aside to let the marchers continue.

Sergeant Vince Lewis of the Phoenix Police Department said in a statement, "Phoenix Police responded to the downtown area for the 'Rally for Justice' demonstration. A specific route was provided to police; however that route was changed and at one point the group expressed intent to march onto the I-10 freeway...A skirmish line was established and non-lethal pepperballs were deployed to move advancing demonstrators back. Three arrests were made of subjects who had thrown rocks at police. Officers were struck on their helmet(s) and protective gear, but no injuries to officers were reported. As many as six injuries to citizens occurred, reportedly related to the pepperballs or fall related injuries.

Meanwhile, at a Black Lives Matter demonstration in Rochester, New York, 74 people were arrested for a variety of charges, including disorderly conduct and resisting arrest, police chief Michael Ciminelli said at a press conference early Saturday.

Chief Ciminelli said 112 officers covered the gathering, including state police and members of town police departments. No officers were injured and there was no property damage, even though some protesters threw rocks at police officers. After the size and intensity of the rally grew, officers eventually were put into protective gear.

It took police officers about three hours to clear the area.

Some of those arrested were detained on sidewalks in handcuffs before being hauled into police vans.

Two locals reporters were arrested but Ciminellu apologized, and they were subsequently released.

In Baton Rouge, hundreds of protesters who descended upon the vicinity of police headquarters clashed with riot gear-wearing officers, who reportedly detained at least a dozen individuals.

A group of protesters formed a human chain on one street, sitting down to block the street. It was then then that two officers tried to grab a young woman (video below), but other protesters wrestled her away. During that scuffle, one officer drew his weapon, upping the intensity of the situation, but the weapon was later reholstered. An officer also pulled out their stun gun and pointed it at a protester.

And in Baltimore, about 200 people assembled at McKeldin Square (below) Friday night, marching from there to police headquarters. After a couple of hours, some members of the group failed to comply with officers and refused to move from out of the roadway, resulting in the arrest of four individuals, according to police.

In Atlanta, a peaceful march of more than a thousand people – organized by the NAACP and Black Lives Matter -- kicked off at Centennial Olympic Park at 6 p.m. and didn’t dissipate for another nine hours, according to ABC Atlanta affiliate WSB-TV. The march was relatively peaceful, with only some protesters blocking an exit to I-75. At 11:25 p.m. Atlanta police chief George Turner said there were no arrests, but by Saturdat morning, WSB-TV was reporting there were a “few arrests.” The exact number remained unknown.

In California, events were held in Los Angeles, San Francisco and Sacramento.

In L.A. rappers Snoop Dogg and The Game led a march to police headquarters, where they met with mayor Eric Garcetti, LAPD chief Charlie Beck and other city officials (below). "We are here to show love and support to the Los Angeles Police Department," Snoop Dogg said. “Thank y’all for allowing us to have conversation. We appreciate it."

About 2,000 protesters marched across downtown San Francisco to a rally outside City Hall under a huge banner that read, "Stop the Racist Police Terror in the U.S."

Black Lives Matter supporters descended upon President Barack Obama's Chicago home, where activist Jedidiah Brown said there is more the president can do to combat deaths of African-Americans at the hands of police.

In another demonstration, activist priest the Rev. Michael Pfleger and actor Nick Cannon led 100 people through the city's violence-plagued Auburn-Gresham neighborhood. "It's very apparent that we're all in pain and we're frustrated," Cannon said.

Other notable demonstrations included those in Detroit's Campus Martius Park, attended by 1,000 people, as well as protests in New York City's Union Square and Omaha, each attended by about 300 people.

In Pittsburgh, 150 people peacefully marched downtown, and in Washington, D.C., a few dozen people rallied outside the U.S. Department of Justice, as well as The White House.

And the Black Lives Matter movement even drew supporters overseas, with hundreds of people marching through central London, as drivers honked their horns in support.

ABC News' Devin Villacis, Rex Sakamoto, Alexandra Faul and Sarah Shales contributed to this report. The Associated Press also contributed to this report.