Chicago police officers at a crime scene in Greater Grand Crossing, one of the city’s most violent neighborhoods, where a 13-year-old boy was shot in both legs in April. Joshua Lott for The New York Times

There was a time when it looked as if Chicago would follow New York and Los Angeles into a kind of sustained peace. Then progress stalled in 2004, and the city has been through some harrowing years leading up to another alarming spike in homicides this year.

Homicide Rate 30 per 100,000 Chicago 25 20 Los Angeles 15 10 New York City 5 1985 1990 1995 2000 2005 2010 2015 30 per 100,000 Homicide Rate Chicago Rate has held steady since 2004. 25 20 Los Angeles 15 10 5 New York City 1985 1990 1995 2000 2005 2010 2015 Homicide Rate 30 per 100,000 Chicago Rate has held steady since 2004. Rate rose from 2014 to 2015 and is on an upward trajectory this year. 25 20 Los Angeles 15 10 New York City 5 1985 1990 1995 2000 2005 2010 2015

Already embroiled in a crisis over race and police conduct, Chicago now faces a 62 percent increase in homicides. Through mid-May, 216 people have been killed. Shootings also are up 60 percent.

So what’s going on in Chicago?

It’s complicated, but a comparison with New York is a good place to start. Both cities began the 1990s with historically high homicide rates; both have diverse populations, including large numbers of blacks, Hispanics and whites, and a wide range of economic fortune as well.

Chicago has about the same population as Brooklyn, but a year’s worth of homicides in the two places shows an astonishing difference in the toll.

400 Cumulative Homicides in 2015 Chicago Longest stretch without homicide: 5 days N.Y.C. 300 200 Brooklyn Longest stretch without homicide: 22 days 100 JAN. APRIL JULY SEPT. DEC. Cumulative Homicides in 2015 Chicago Longest stretch without homicide: 5 days 400 N.Y.C. 300 200 Brooklyn Longest stretch without homicide: 22 days 100 JAN. APRIL JULY SEPT. DEC. 400 Chicago Longest stretch without homicide: 5 days Cumulative Homicides in 2015 New York City 300 200 Brooklyn Longest stretch without homicide: 22 days 100 APRIL JAN. FEB. MARCH JULY DEC. NOV. OCT. SEPT. JUNE MAY AUG.

Guns Are a Key Difference

People who know both cities say there are some significant differences in policing, especially around the issue of guns.

The homicide rate in Chicago is just a little higher than in New York when guns aren’t involved. But when it comes to shootings, both fatal and not, Chicago stands out, suggesting a level of armed interaction that isn’t happening in New York.

Number per 100,000 people Homicide by means other than firearm Chicago New York Homicide by firearm Nonfatal shootings 0 20 40 60 80 100 Number per 100,000 people Homicide by means other than firearm Chicago New York Homicide by firearm Nonfatal shootings 0 20 40 60 80 100

Chicago has a reputation for strict gun laws, and gun rights advocates often point to it as proof that gun regulation doesn’t reduce violence. But its laws aren’t what they used to be: Federal courts struck down its ban on handgun ownership in 2010, and its ban on gun sales in 2014. And a New York Times analysis showed guns were easily available from nearby jurisdictions, especially Indiana.

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And Chicago is more lenient about illegal handguns than New York, prescribing a one-year minimum for possession versus three and a half years in New York. An attempt to match the New York law in 2013 was rejected by the Illinois legislature out of concern for skyrocketing incarceration rates for young black men.

New York also hired a lot more police officers in response to the crime of the 1990s, and, during its stop-and-frisk era of the 2000s, steeply increased gun enforcement. Recent studies, including one that looked at increased police presence in London after a terrorist attack, have suggested more police might mean less crime, said Jens Ludwig, the director of Crime Lab at the University of Chicago, which studies crime in both Chicago and New York.

Chicago’s Police Department, overwhelmed, can respond only to the most serious problems, leaving citizens to feel responsible for their own security, he said.

“Everyone has to establish deterrence on a retail basis,” he said. “People carry guns in public because other people are carrying guns. It’s literally an arms race, a vicious cycle. There are lots of indications that New York City, by taking guns more seriously and hiring more officers, has gotten a lot of guns off the streets, creating a virtuous cycle.”

+100% 600 New York City New York City +75 Chicago +50 400 Police Force Per 100,000 Change in Weapons Cases Since 2001 +25 200 –25 Chicago ’90 ’95 ’00 ’05 ’10 ’14 ’01 ’03 ’05 ’07 ’09 ’11 ’13 ’15 New York City New York City +100% 600 +75 Chicago +50 400 Police Force Per 100,000 Change in Weapons Cases Since 2001 +25 200 –25 Chicago ’90 ’14 ’01 ’15 +100% New York City 600 New York City +75 Chicago +50 400 Police Force Per 100,000 Change in Weapons Cases Since 2001 +25 200 –25 Chicago 1990 1995 2000 2005 2010 2014 2001 2003 2005 2007 2009 2011 2013 2015

Gang Wars in Chicago Drive Much of Its Violence

In Chicago, gang disputes are clearly a big part of homicides, said John Hagedorn, a professor at the University of Illinois at Chicago who studies Chicago gangs. “But these are not the same kind of disputes as before – they’re more localized disputes.”

Many of Chicago’s gangs have fractured, leading to more violence, said Arthur Lurigio, a criminology professor at Loyola University Chicago. While Latino gangs have remained more hierarchical, black gangs have splintered into small, disparate factions, whose disputes are less over territory and profits, and more over personal insults or shames, often fueled by social media, he said.

“Young people are making a lot of indirect threats toward cliques and rival gangs that are being interpreted as being threatening,” said Desmond Patton, a professor at Columbia University who has studied violence on social media. “Tagging is the conversation starter that could lead to someone getting a gun.”

In addition to making threats, individuals at times post their location on social media to prove to rivals that they’re tough, he said.

In one well-known instance, Gakirah Barnes, a Chicago gang member who was rumored to have killed or shot up to 20 rival gang members, referenced an address she frequented on Twitter. In the tweet, provided by Dr. Patton, Ms. Barnes says “Lz,” which has multiple meanings in Chicago gang cultures, including living life, at address number 6347. Later that day, she was shot and killed near the address.

Tweet from Gakirah Barnes’s account

Gangs figure in many homicides in New York as well, but recent polls by The New York Times suggest that the gang problem may be worse in Chicago.

Chicago How likely is it that a young person in your neighborhood will be in a gang? VERY LIKELY SOMEWHAT LIKELY NOT LIKELY BLACK HISPANIC WHITE Chicago How likely is it that a young person in your neighborhood will be in a gang? SOMEWHAT LIKELY NOT LIKELY VERY LIKELY BLACK HISPANIC WHITE

Although there were differences in the way the polls were conducted, blacks and Hispanics in Chicago expressed significantly less hope than their counterparts in New York that their children would escape gang life.

New York City How likely is it that a young person in your neighborhood will be in a gang? ALMOST CERTAIN VERY LIKELY TOSSUP NOT LIKELY BLACK HISPANIC WHITE New York City How likely is it that a young person in your neighborhood will be in a gang? ALMOST CERTAIN VERY LIKELY TOSSUP NOT LIKELY BLACK HISPANIC WHITE

Dr. Hagedorn also points out that though the city also has a lot of Latino gang members, Chicago’s violence is much higher among African-Americans. Three quarters of all homicide offenders and victims are black, he said.

“The shootings today are more spontaneous over day-to-day humiliations of youthful African-Americans,” he said.

Crime Persists in Chicago’s Most Segregated Neighborhoods

Whether exacerbated by gangs or guns, though, Chicago’s killings are happening on familiar turf: Its poor, extremely segregated neighborhoods on the South and West Sides. And many say that is Chicago’s real violence issue.

“Where do gangs come from? They tend to take root in the very same neighborhoods that drive these other problems,” said Robert J. Sampson, a professor at Harvard and the author of “Great American City: Chicago and the Enduring Neighborhood Effect.” “You can’t divorce the gang problem from the problem of deep concentrations of poverty.”

“What predicts violent crime rates is concentrated poverty and neighborhood disadvantage, and what determines concentrated poverty is high levels of black segregation combined with high levels of black poverty,” said Douglas S. Massey, a sociology professor at Princeton University.

In Chicago, homicide rates correspond with segregation. While many areas have few or no killings, the South and West Sides are on par with the world’s most dangerous countries, like Brazil and Venezuela, and have been for many years.

O’HARE INTERNATIONAL AIRPORT O’HARE INTERNATIONAL AIRPORT CHICAGO LINCOLN PARK AUSTIN GARFIELD PARK Homicide rate per 100,000 in 2015 Most segregated areas Where the chance that any two residents are of different races is less than 10 percent 20 50 10 2 ENGLEWOOD WEST PULLMAN ROGERS PARK O’HARE INTERNATIONAL AIRPORT O’HARE INTERNATIONAL AIRPORT CHICAGO LINCOLN PARK NEAR NORTH SIDE AUSTIN GARFIELD PARK NORTH LAWNDALE Most segregated areas Where the chance that any two residents are of different races is less than 10 percent Homicide rate per 100,000 in 2015 20 50 10 2 ENGLEWOOD GREATER GRAND CROSSING CHATHAM WEST PULLMAN CHICAGO AUSTIN ENGLEWOOD Homicide rate per 100,000 in 2015 Most segregated areas Where the chance that any two residents are of different races is less than 10 percent 20 50 10 2 CHICAGO Most segregated areas Where the chance that any two residents are of different races is less than 10 percent Homicide rate per 100,000 in 2015 20 50 2 10

The linkage of segregation, poverty and crime exists in New York City as well. Homicides occur at higher rates in parts of Brooklyn, the Bronx and Harlem, and many other neighborhoods are virtually free of killings.

Homicide rate per 100,000 in 2015 Most segregated areas Where the chance that any two residents are of different races is less than 10 percent BRONX 20 50 10 2 MANHATTAN NEW YORK CITY QUEENS BROOKLYN STATEN ISLAND Most segregated areas Where the chance that any two residents are of different races is less than 10 percent Homicide rate per 100,000 in 2015 BRONX 20 50 10 2 MANHATTAN NEW YORK CITY QUEENS BROOKLYN STATEN ISLAND BRONX MANHATTAN NEW YORK CITY QUEENS BROOKLYN STATEN ISLAND Most segregated areas Where the chance that any two residents are of different races is less than 10 percent Homicide rate per 100,000 in 2015 20 50 10 2 NEW YORK CITY Most segregated areas Where the chance that any two residents are of different races is less than 10 percent Homicide rate per 100,000 in 2015 20 50 2 10

But segregation in New York is nothing like in Chicago: The perfectly isolated neighborhood – where every man, woman and child is the same race – is rare in New York. Less than one percent of the population lives in such areas, and most of them are white. In Chicago, 12 percent of the black population is in a census block group that is 100 percent black.

Racially segregated minority neighborhoods have a long history of multiple adversities, such as poverty, joblessness, environmental toxins and inadequate housing, Professor Sampson said. In these places, people tend to be more cynical about the law and distrust police, “heightening the risk that conflictual encounters will erupt in violence.”