President Donald Trump told generals this week that cities such as Chicago are “under invasion from within” and must be crushed with force, serving as a training ground for American troops. “We’re going in,” he declared. Protests have already sprung up in response, and in Broadview just outside Chicago, federal agents on multiple days have fired tear gas and pepper balls at demonstrators and journalists standing dozens of feet from an Immigration and Customs Enforcement facility. History and science warn: When federal police use force to suppress dissent, larger and more violent protests follow.
With each use of chemical agents — tear gas and pepper spray — 2% more protests, 5% larger crowds, more property damage, three more injuries to protesters and two more injuries to police occur in the days that follow, I find in my newest paper, based on Harvard University’s Crowd Counting Consortium. Police use of rubber bullets has a similar effect: 6% more protests, 29% larger crowds, more property damage, five more injuries to protesters and two more injuries to police. Mass arrests and government suppression of free speech similarly inflame protests. These are not isolated blips but part of a vicious cycle of violence.
To see why, consider two philosophies of policing. Escalated force means aggressive tactics — tear gas, rubber bullets, baton charges, mass arrests, militarized gear — meant to break up crowds and crush dissent. Negotiated management, by contrast, treats protests as political expression, protected by the First Amendment. It emphasizes communication, de-escalation periods, trust, working with protest organizers and a visible but nonmilitarized police presence. In practice:
- Escalated force provokes. Negotiated management prevents.
- Force tells crowds they are enemies. Negotiation treats them as citizens.
- Police use of force sparks cycles of retaliation. Negotiation channels energy back into dialogue.
Chicago’s history makes the difference painfully clear. At the 1968 Democratic National Convention, Mayor Richard J. Daley denied protest permits, dispatched riot police and erected barricades. The result was violence, mass arrests and a lasting image of a city at war with its own people. After federal commissions warned against these tactics, many U.S. cities in the 1970s shifted toward negotiated management, and protests became calmer.
Yet Chicago has periodically returned to the hard-knuckles approach, often with more harm than good. The George Floyd protests in 2020 showed the same pattern nationwide: Escalated force was followed by greater unrest, while negotiated management saw fewer confrontations.
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Two fellow professors and I made this point before in the Tribune. Ahead of the 2024 Democratic National Convention in Chicago, before the Republican convention in Milwaukee and during campus protests over free speech, we argued that when authorities use excessive force, protests intensify and violence escalates. When they negotiate and work with protest organizers, as they did in 2024, protests are protected and peaceful. Chicago now stands at that same crossroads.
Editorial: State and local officials must do more to safeguard Broadview protesters
The federal attack on Chicago is already underway. First, Operation Midway Blitz brought hundreds of ICE agents who have already arrested 550 people in the Chicago area. Next, Border Patrol agents were sent to downtown Chicago. Gov. JB Pritzker rightly observed: “All of this has been aimed at causing chaos and mayhem in the hopes of creating a pretext to deploy military troops against Chicago.” Now the administration of Donald Trump has escalated again with plans to deploy 100 National Guard troops in Illinois. In every case, these forces come from outside the state, wear masks and have no relationship with the people of Chicago. Such deployments erode legitimacy and fuel backlash — they are the very opposite of what research and history show is effective.
Chicago officials, including Mayor Brandon Johnson, have rightly pushed back, refusing to cooperate with federal immigration enforcement and forbidding Chicago police from wearing masks. That is the right instinct. Our research shows that negotiated management — visible, accountable officers who build trust with community leaders — reduces conflict. Masked units and military gear, by contrast, send a message of occupation and provoke confrontation. Chicago must hold firm against these federal tactics.
The role of law enforcement is clear: to serve and protect, not enable federal escalation. That means rejecting militarized policing and standing between Chicagoans and outside forces who would inflame unrest.
Chicago can still model a different path — one that stands up for municipal sovereignty, defends democracy, protects its people and treats protesters not as enemies but as citizens exercising their rights.
David White is an associate professor of mathematics at Denison University.
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