If President Donald Trump follows through on his threat to send National Guard troops to Chicago — over the objections of Gov. JB Pritzker and Mayor Brandon Johnson — then it would be unprecedented.

“In Illinois, we are not aware of the state’s National Guard forces ever being federalized for an in-state response without the Governor’s request and concurrence,” wrote Illinois National Guard public affairs officer Lt. Col. Bradford Leighton in an email to the Tribune.

Trump threatened in a tweet in January 2017 to “send in the Feds!” in response to violence in Chicago. Ultimately, he didn’t.

A review of the Tribune’s archives produced 18 events in which the governor activated the National Guard within Chicago. Two of them — both during the 19th century — involved a sitting U.S. president who acted in coordination with the governor.

The National Guard has been activated to Chicago 18 times from 1877-2021. Here’s a breakdown.

“The Pullman Strike (1894) and Railroad Strike (1877) were both considered state active duty,” said Adriana Schroeder, command historian for the Illinois National Guard. “Both of those involved the union, spread throughout the United States, and drew the attention of the president who was in close communications with the governors of the affected states.”

On occasion, state and city officials have disagreed if a National Guard response was warranted.

In 1992, Chicago Housing Authority Chairman Vincent Lane requested Mayor Richard M. Daley activate the National Guard to help sweep the Cabrini-Green public housing development after a sniper killed 7-year-old Dantrell Davis, but that ultimately wasn’t part of Daley’s 11-point plan. Violence in the city during 2008, prompted then-Gov. Rod Blagojevich to offer troops, but Mayor Daley refused to accept them.

Here’s a look back at five times when the National Guard was enlisted for assistance in Chicago.

Great Railroad Strike (1877)

President Rutherford Hayes deployed the Army in city after city throughout the East and Midwest because of a railway strike, joining with local militias to restore order. Strikers viewed militiamen and soldiers as strikebreakers, and with the arrival of troops in Chicago, the violence escalated dramatically, as did civilian deaths. Thirty people were killed in Chicago from July 23-26, 1877.

Race riots (1919)

Black teen Eugene Williams floated on a wooden tie past an invisible, but mutually understood, line that separated a Black beach at 29th Street from a white beach at 26th Street. White youths threw rocks at him, according to later investigations, and Williams, who could not swim, was hit and drowned.

Although several people, white and Black, tried to revive Williams, a police officer at the 26th Street Beach was unwilling to arrest the rock throwers on the word of their Black accusers or to help Williams.

Unequal justice proved to be the rule during the ensuing violence, which killed 38 people — 23 of them Black, 15 white. The four-day chaos was finally ended by the Illinois militia and a cooling rain. Williams is buried in Lincoln Cemetery in Blue Island.

Riots after the assassination of Rev. Martin Luther King Jr. (1968)

On April 4, 1968, the Rev. Martin Luther King, Jr. was assassinated in Memphis, Tenn. As the tragic news spread, riots and looting took place in cities including New York, Washington, Nashville, Tenn., and Raleigh, N.C. In Chicago, on the first night of rioting, nine people, all Black, were killed.

Two days later, with the approval of Mayor Richard J. Daley, the U.S. Army was called in and thousands descended on the city’s troubled areas. When the fires died out, 162 buildings had been destroyed, 12 people killed and 3,000 arrested.

Leighton said the response, “started as a state active duty mission for the first two days but, at the request of the Governor, the Illinois National Guard forces were placed on federal orders for the remainder of the response.”

More than 9,900 soldiers and airmen were activated from April 5-13, 1968, Leighton said.

Democratic National Convention (1968)

Vice President Hubert H. Humphrey was nominated at the stormy convention that was marked by riots on the streets as well as raucous political demonstrations on the floor of the Chicago Amphitheatre.

Gov. Samuel Shapiro ordered the National Guard to assist the almost 12,000 Chicago police officers, 1,000 federal agents and 7,500 U.S. soldiers already on duty to maintain law and order during the convention. Almost 10,000 members of the Illinois National Guard responded, Leighton said.

‘Days of Rage’ (1969)

Starting on a Wednesday night in a field in Lincoln Park where a year before thousands of demonstrators had clashed with police during the 1968 Democratic National Convention, the self-proclaimed Days of Rage were meaner, better planned and more violent.

On the night of Oct. 8, 1969, hundreds of demonstrators summoned to Chicago by leaders of the radical Students for a Democratic Society to protest the ongoing Chicago 8 trial of the leaders of the convention riots erupted into a destructive orgy of violence.

They marched down LaSalle Street toward the Drake Hotel, aiming, they said, for the nearby residence of U.S. District Judge Julius Hoffman, who was presiding over the Chicago 8 trial.

Confronted by police, the demonstrators never made it to their target, but along the way, they left hundreds of thousands of dollars in damage in broken windows, wrecked cars and medical costs.

The next morning, commuters on the Chicago Transit Authority’s 151 bus route gagged on the remnants of the tear gas that had drifted over Michigan Avenue. Meanwhile, more than 2,500 National Guard members took to the streets.

Later that Thursday, a demonstration at the Gen. John Logan statue in Grant Park, the site of a famous 1968 convention riot, was nipped in the bud by cautious police. On Friday, the demonstrations were muted and peaceful.

But on Saturday, the most outrageous Day of Rage arrived.

Hundreds of hard-core protesters gathered on Randolph Street at the site of the Haymarket Square statue of a policeman that had been damaged by a late-night explosion just five days earlier.

Accompanied by an army of police, the marchers walked east on Randolph to LaSalle, where they turned south, ostensibly on a circuitous Loop march to Grant Park.

But at LaSalle and Madison streets, the demonstrators broke ranks, clashed with police and headed east on Madison, breaking store windows and fighting with police in a vicious melee that resulted in nearly 300 arrests, 48 police injuries and unknown more to protesters.

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