Chicago’s mayor, Lori Lightfoot, said she woke up in shock and pain for her city on Monday, after crowds overnight broke windows and looted stores in the north side shopping area known as the Magnificent Mile.

Following a contentious situation 10 miles away on the city’s south side on Sunday, where police shot a 20-year-old Black man in the back, wounding him, more than 100 people were ultimately arrested in the trouble that flared, apparently in retaliation for the shooting, in the upscale business district.

For many of the city’s residents, the events were not so much a shock as a social time bomb going off that had been ticking louder and louder since the spring.

While the destruction at the flagship stores made national headlines, weeks of smaller-scale eruptions on the south and west sides of the city had garnered relatively little attention, along with a surge in gun violence, amid a public health, economic and policing crisis crushing already poor neighborhoods.

Joseph Williams, a Black south sider, father of five and community organizer, found himself at a nexus on Sunday when he saw a crowd gathering in his neighborhood after the latest police shooting. He was alerted by a Facebook live stream, he said, and came across an all-too familiar incident.

“Minutes after I arrived, I watched [the police] pull a man under the crime scene tape and beat him bloody on the sidewalk. Then they put him in the police car like he was the one that did something wrong,” Williams told the Guardian.

Williams said he was no stranger to poverty and police violence.

He sees decades of investment in some parts of the city and systemic deprivation in others, like his own, a majority Black community, where life expectancy is 30 years less than for those living on Chicago’s north side, home of the Magnificent Mile.

“When you look at how the system was built, it was never built for our communities to really be successful. The pandemic is showing us that,” he said.

Usually on Sundays, one of his biggest challenges is finding the perfect Netflix show to watch with his kids, but after the shooting he spontaneously found himself at the center of mediation efforts between distraught residents and more than 100 officers, some armed with assault rifles, after the police shooting.

Williams, who runs an organization that supports south side fathers, was able to help other organizers at the scene bring down tensions by forming what he called a “peace wall” between angry south siders and the police. People gradually dispersed, and he went home.

Then on Monday the police chief, David Brown, cited social media posts that had called on people to go north to the Magnificent Mile to cause havoc.

And Lightfoot decried “brazen criminal looting and destruction” at a press conference.

Page May, co-founder of Assata’s Daughters, a radical Black women’s grassroots organization, said: “Chicago has this unique dissonance in calling itself a progressive place because of Obama and having a Black gay woman as mayor. But when you have incredible police violence and an apartheid level of segregation and divestment, communities are forced to fend for themselves in ways that politicians don’t like.”

The resurgence of the Black Lives Matter movement in the wake of George Floyd’s killing in Minneapolis in May led to nationwide protests and in Chicago has put the spotlight back on the police department, which has a track record of racial bias and brutality going back years.

Since 1964, Chicago has nearly tripled per capita police spending, recent analysis showed, making it the third-largest police force in the country and the largest in proportion to the city population.

After the Fourth of July holiday weekend ended with 17 people fatally shot and 63 more wounded in a surge of gun violence, the Rev Gregory Livingston, who ran an anti-gang organization on the south side until last summer, warned of a woeful “tale of two cities” in Chicago and a legacy of “corruption and racism” exacerbated by coronavirus and the economic fallout.

“There is an individual responsibility [among those shooting], but there are also conditions that create a climate of violence,” he said at the time, and called on the mayor to tackle inequality “head on”.

As the pandemic has uprooted life across Chicago and across America, Lightfoot has won praise for her decisive leadership, often going viral for her tweets supporting social distancing.

But while the mayor initially praised protests over Floyd’s killing as “righteous anger” referring also to some Chicago police killings, this was countered by the suspension of free school meals, aggressive policing and halting public transportation.

May accused her of running the city under a “progressive facade”.

In June, city council members pleaded with Lightfoot to help them protect their communities and businesses from the clashes protesters were having with police and damage to property and businesses.

The council’s Black Caucus accused the mayor of using national guard to protect the central business district while leaving south and west side communities exposed to chaos and damage, a suggestion Lightfoot said “offends me deeply, personally, in part because it is simply not so”.

But Michelle Harris, alderman for the eighth ward on the south side, asked how she could convince businesses to rebuild there.

“It’s like, what are we going to have left in our community? Nothing,” she said.

Since March, Chicago’s unemployment rate has grown to 15.6%, according to the Bureau of Labor Statistics. Estimates show that on the south side the unemployment rate is more than double that, while on the north side it is below 10%.

Last week the city announced that a record $926m, more than a third of the city’s tax revenue, would be funneled into new investments via a complex and controversial special property taxing program that funds services such as new roads and job training but has long been criticized as favoring high-end communities and developers.

Meanwhile poorer Black and brown communities were asked to compete for a single $10m “Chicago Prize” to fund one community-led initiative to transform their neighborhood.

In April the mayor got into a housing assistance row, revealed in a leaked call with council members.

And while on that call she prioritized the supply of hospital beds, given the pandemic, but now there are concerns of an impending “healthcare desert” on the south side with a hospital slated to close after failing to get state funding to form a bigger system with other hospitals. If the closure goes ahead next year it will be the third such closure of a hospital in a majority Black neighborhood in two years.

And this against a backdrop of other yawning inequalities that stoke gun violence. More than 2,200 people have been shot this year in the city, nearly 700 more than in the whole of 2019.

Now Lightfoot, who previously vowed to turn away federal agents, agreed to the Trump administration’s proposal of sending 200 federal agents to the city, despite the problems they created in Portland, Oregon. Such agents should not be confused with the federal investigators already on the ground in Chicago who earlier this month scored a significant gang bust.

The idea of militarized federal law enforcement agents descending on Chicago on the orders of Donald Trump’s Operation Legend is another thing entirely and community organizer Williams feared they would be more harm than help.

“None of these people actually want to build relationships with these communities. They don’t want to get to know us, so why do they get to have this job, carry deadly weapons and police us?” he said.

Black Lives Matter-Chicago, the Black Abolitionist Network and Good Kids Mad City, a youth anti-violence nonprofit, want the city to defund the police and cancel the $33m contract between police and Chicago public schools, in order to move much-needed funding to other needs on the South and West Sides.

On Saturday morning, before the eruptions on Sunday, mothers led a rally calling for police reform and an end to brutality. On Monday, members of Black Lives Matter-Chicago also held a rally, calling for police funding to be diverted to education, jobs, housing, healthcare and other public services, and issued a statement.

It read, in part: “Over the past few months, too many people – disproportionately Black and brown – have lost their jobs, lost their income, lost their homes, and lost their lives as the city has done nothing and the Chicago elite have profited.

It continued: “When protesters attack high-end retail stores that are owned by the wealthy and service the wealthy, that is not ‘our’ city and has never been meant for us.”

Williams told the Guardian he wanted a city where his children “can enjoy life” and where city leaders don’t perpetuate and intensify disparities between “up north” and “down south”.

“If there is going to be one Chicago, make it one Chicago,” he said.