On Tuesday, swaths of East and West Baltimore erupted in flames amid riots that followed the funeral for Freddie Gray, a 25-year-old man who died a week after suffering a critical spine injury while in police custody. In a startlingly segregated city struggling with failing schools, failing infrastructure, a failing economy and a police department under federal investigation, it seemed only a matter of time before this side of Baltimore boiled over.

Here are some key things to know about this city of 622,000:

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HOUSING

Homelessness and poverty are pervasive problems. Roughly 23 percent of the city is living below the poverty line, while unemployment is much higher than the national average. Late last year the city's housing authority opened its lottery for public housing for the first time in 10 years. Within a week, roughly 60,000 people — nearly 10 percent of the city's population_had signed up. Baltimore is also a city of neglect, with roughly 17,000 abandoned row homes. In Sandtown, where Gray was raised and later arrested, whole city blocks sit vacant and neglected among empty lots overgrown with grass and littered with trash.

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URBAN DEVELOPMENT

Baltimore was once a prosperous city, celebrated by journalist H.L. Mencken. It was a manufacturing dynamo, famed for the rye whiskey and straw hats it made, among other things. But the story of Baltimore is much the same as the rest of urban America since World War II: Industry left, and fortune followed.

Since the 1950s, the city's population has steadily declined, dwindling from nearly 1 million to 622,000. The city saw growth for the first time in six decades when it gained more than 1,000 residents in 2012; the next year, the count slightly declined.

The upheavals of the 1960s and '70s contributed to the disintegration. Rioting after the Rev. Martin Luther King Jr.'s death in 1968 left scars on the landscape that have never healed, and strikes by police, teachers and municipal workers in 1974 hastened the city's decline.

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DRUGS AND POLICE

In the 1990s, the crack cocaine and heroin trade was so robust that a federal study cited Baltimore as one of the country's most drug-addled cities. Its reputation remains the same. Drugs and crime prompted former governor Martin O'Malley to institute a "zero tolerance" policing policy once he became mayor of Baltimore in 2000, which many site as fanning the flames for mistrust between police and members of poor black communities.

In 2010, the ACLU and NAACP reached an $870,000 settlement with the city that required police to track their arrests. But by 2012, an independent auditor found Baltimore officers still couldn't justify 35 percent of their arrests.

"When we adopted zero tolerance policing we were embedding in the police culture this mindset of being at war with the citizenry," said Sonia Kumar, an attorney at the ACLU. "At no point since then has that mindset been disrupted or challenged in any meaningful way."

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EDUCATION AND OPPORTUNITY

Some experts say the frustration and discontent among Baltimore residents stems from the lack of educational opportunities. The city's failing school system, which was under a federal consent decree for more than 20 years over treatment of special needs students, has fueled a sense of desperation among the city's youth, as well as resentment, restlessness and anger, according to Rashawn Ray, a sociology professor at the University of Maryland, College Park.

"They are reacting to something very specific: a feeling of hopelessness," Ray said. "People who aren't from these neighborhoods see one incident: Freddie Gray. But here, Freddie Gray triggers collective memory and experiences that they've had over time, like their lives don't matter. People without jobs, trying to feed their families in neighborhoods without grocery stores. Sitting around not talking about, 'What did you do at school today?' but 'Did you get stopped by the police on your way home?' It's been brewing for decades."