On the opening day of the Democratic National Convention (DNC), thousands of marchers took to the streets for a mostly peaceful protest, calling for a ceasefire in Gaza and an end to US support for Israel.
But dozens were arrested when several demonstrators breached the security fence surrounding the Chicago site.
The turnout was lower than the tens of thousands that organizers had hoped for.
The protest highlights one of the most contentious issues on the left of American politics: American support for Israel's war in Gaza.
Monday's march unfolded as President Joe Biden made a brief appearance at the United Center, the sports venue that will host this week's DNC, just hours before his address to party faithful.
At one point during the protest, a small group of pro-Palestinian demonstrators broke down the fence surrounding the conference's security perimeter and fled.
Chicago police said the protesters did not breach the inner security fence and the situation was quickly brought under control. At least four people were arrested.
Demonstrators chanted slogans including “From the river to the sea, Palestine will be free,” which anti-Semitic watchdogs say is an anti-Semitic call for the destruction of the state of Israel. Pro-Palestinian activists reject the slogan as hateful.
Earlier, a small group of pro-Israel protesters gathered briefly at the edge of Union Park, where the pro-Palestinian march began and ended.
Many of the Gaza war demonstrators said they saw little difference between Mr Biden and his running mate Kamala Harris, who formally accepted the Democratic White House nomination this week after withdrawing from the presidential race last month.
“The Democratic Party may present a new face, but its support for Israeli oppression remains unchanged,” said Omar Younes, co-founder of Jizoor, a Palestinian youth organization in Chicago.
Another opponent, Tallis George Munro, said he would definitely vote for Ms Harris and her husband Tim Walls, but did not want to give them a “free pass” on their support for Israel's war in Gaza.
Mr Munro, from Cleveland, Ohio, said he was deeply concerned about the policies of Republican candidate Donald Trump – which he described as a “huge threat”.
“We're closer to white Christian nationalism with Trump,” he said. “That's the biggest problem in this country right now.”
Other protesters told the BBC they would either vote for Green Party candidate Jill Stein or not at all.
Marchers were asked by independent presidential candidate Cornel West, a philosophy professor and left-wing activist.
“This is not about some Machiavellian politics or some utilitarian calculation about elections,” he told the crowd. “It's about morality.”
The parade attracted people from neighboring states and abroad. Karina Lemus was in attendance as a member of the Colorado Springs People's Coalition.
He said he has been involved in the Palestinian rights movement for decades.
“I'm sure they'll ask us in,” he said of the DNC delegates.
Protests will continue throughout the rest of the week during the conference.
The Israeli military launched a campaign in Gaza to wipe out Hamas in response to an unprecedented attack on southern Israel on October 7, during which approximately 1,200 people were killed and 251 taken hostage.
More than 40,000 people have been killed in Gaza since then, according to the territory's Hamas health ministry.