CHICAGO — Thousands of protesters marched through downtown Chicago on Sunday in one of the city's largest demonstrations in years, airing grievances about war, climate change and a wide range of other complaints as world leaders assembled for a NATO summit.
At least 45 people were arrested and four police officers were injured, authorities said.
The protest, which for months had stirred worries about violence in the streets, drew together a broad assortment of participants, including peace activists joining with war veterans and people more focused on economic inequality. But the diversity of opinions also sowed doubts about whether there were too many messages to be effective.
And some of the most enduring images of the event were likely to be from the end — when a small group of demonstrators clashed with a line of police who tried to keep them from the lakeside convention center where President Barack Obama was hosting the gathering.
The protesters tried to move east toward McCormick Place, with some hurling sticks and bottles at police. Officers responded by swinging their batons. The two sides were locked in a standoff for nearly two hours, with police blocking the protesters' path and the crowd refusing to leave. Some protesters had blood streaming down their faces.
Authorities were seen making arrests one by one and leading individual demonstrators away in handcuffs.
After the clash near McCormick Place, Chicago police Superintendent Garry McCarthy said at a news conference that the protests of the summit resulted in 45 people being arrested and four officers suffering injuries — one from a stab wound in the leg. Those numbers seemed certain to rise as new clashes erupted later in the night.
Hundreds of protesters gathered late Sunday night near the Art Institute of Chicago as first lady Michelle Obama hosted a dinner for spouses of NATO leaders inside. At least 100 Chicago police officers in riot gear were also at the scene.
Earlier at the protest near McCormick Place, Esther Westlake, a recent graduate of Northeastern Illinois University, marveled at the size of the crowd. She said she had been involved in marches protesting the Iraq war in Chicago but never one this big.
"It's crazy. There's so many people here," she said. "Having NATO in town is kind of exciting."
But she wondered whether the political agendas of the protesters were too unfocused to get diplomats' attention.
"It seems like there's so many messages and people aren't really sure what they want to get accomplished," Westlake said. "People just need to figure out what their argument is going to be."
She worried that some protesters participated simply "to do stupid things" and cause trouble.
Some participants called for the dissolution of NATO.
"Basically NATO is used to keep the poor poor and the rich rich," said John Schraufnagel, who traveled from Minneapolis to Chicago for the march. Since the end of the Cold War, he said, the alliance has become "the enforcement arm of the ruling 1 percent, of the capitalist 1 percent."