Chicago is the biggest city in the American Midwest. It's full of gangsters, burning railways, corrupt politicians, and, on occasion, robots.
Transformers: Dark of the Moon[]
After taking Carly Spencer captive, Dylan Gould headed to Chicago. Sentinel Prime also headed to Chicago to set up few of the space bridge pillars. Needing privacy to conduct their work, Megatron ordered a huge Decepticon invasion force take over Chicago. Several motherships arrived to disgorge a large number of Orbital Assault Carriers, while ground forces took to the streets. A huge portion of the city's population was slaughtered when the Decepticons sealed off the city. Sam Witwicky headed there to rescue Carly with the help of the ex-NEST soldier Robert Epps and a few other ex-NEST comrades. After taking a look at the Decepticon-fortified Chicago, Robert Epps realized that they had no chance of surviving all that, but Sam pressed on. As Epps attempted to dissuade Sam from rescuing Carly, Sam asked what they should do, and Epps admitted that they had to give up. Soon afterward, an Orbital Assault Carrier attacked the group. Just after killing several civilians and nearly killing Sam and Epps, the fighter was shot down. Sam and Epps looks behind them to see their savior—Optimus Prime, who gave his own answer to Sam's question: kill every last Decepticon. The Wreckers Leadfoot, Topspin, and Roadbuster proceeded to execute the pilot by tearing it to pieces.
Optimus then explained why they had feigned departure; they needed to fool the world's leaders that they were gone, so they could see the truth behind the Decepticons. As the rest of the Autobots arrived on scene, Sam inquired as to how they survived, to which Roadbuster and Leadfoot explained that the Autobots hid in the boosters of their ship, the Xantium which splashed in the Atlantic, and then they traveled to Chicago from there. Wheelie and Brains then reiterated that Autobots would never leave Earth, and Optimus announced that they needed an element of surprise, to which Sam said he knew where to look.
Asking if Bumblebee could fly the downed Orbital Assault Carrier (which he replied with a hand shrug) Bumblebee and Sam departed for Dylan Gould's penthouse suite. Inside, Carly observed an argument between Sentinel and Megatron on the other building using a telescope. Sneaking in through the balcony, Sam confronted Gould, but Laserbeak attacked Sam as Carly appeared, then threw him over the balcony. Bumblebee's captured Orbital Assault Carrier caught Sam, who urged Carly to jump. With the boy and his girl safely secured, Bumblebee opened fire on the human collaborators, but Laserbeak sent a mini-drone dispatched by the United States military into one of the Orbital Assault Carrier's thrusters, then attacked Sam. Pinning Laserbeak above the gun turret, Sam told Bumblebee to fire, killing the aerial Decepticon before they crash-landed onto the ground. As Dylan frantically ran about the streets shouting that the Autobots were alive, Megatron ordered the Decepticon to raise the bridges into the city and find the Autobots.
Reuniting with the Autobots and ex-NEST soldiers, the group was able to use the mini-drone to warn the powers that be about Sentinel and Megatron's plan to transport Cybertron to the Sol System. Colonel William Lennox mobilized NEST for a drop into a city using wing suits. Realizing that they had to destroy the pillars, Epps team and the Autobots head into the city, but were attacked by Shockwave and the Driller, separating Prime from his trailer carrying his weapons. Optimus agreed to take the Autobots on a diversionary attack while Epps and his team made their way to a skyscraper with the necessary height and clear line of fire, but not before Que gave them some urban combat weapons, the boom-sticks and grapple gloves. In distracting Shockwave, Wheelie and Brains became separated from the Autobots.
Following this, Lennox and the NEST forces arrived in the city, but were forced to wing-suit in. As Starscream lead the aerial counter-attack, the NEST soldiers abandoned the plane, gliding away until they lost the Decepticons in a tilted building. Once Epps team made their way to the right floor for the shot, the Decepticon Orbital Assault Carriers began shooting the building, causing the portion above the line of fire to begin collapsing. A Decepticon scout jumped into the building, forcing Epps to throw a grenade to distract it long enough for the humans to slide down the windows, just barely falling into the floors below. One soldier was not so lucky, and the debris fell around Shockwave. Knowing that there were humans inside, Shockwave ordered the Driller to begin eating the building, causing it to collapse onto another nearby building. As the humans evacuated onto the fire-escape on the other building, Optimus Prime, having recovered his flight tech, managed to kill the Driller, saving the humans from pursuit. Furious with the death of his pet, Shockwave fired a cluster of missiles at Optimus, causing him to become tangled in some cables as the Wreckers came to his rescue.
At this point, Sentinel Prime gave the order to launch the pillars into orbit, at the same time as Wheelie and Brains discovered a downed Orbital Assault Carrier. While Epps and his team made their way through the streets, Sam and Carly continued on in another direction. To a position where Starscream spotted them. Relishing a chance to torment a long thorn in the Decepticons side, Starscream had some fun tormenting and threatening Sam. This allowed Sam a chance to use the grapple glove given to him by Que, hitting the Air Commander's right optic. Starscream began flailing around in pain, tossing Sam through a window, which allowed him to arm a boom-stick. The commotion attracted the attention of Lennox and the NEST forces. Just as Lennox arrived, Sam managed to jump on Starscream's head and jam the boom-stick into his left eye. Now completely blind, Starscream lost whatever control he had left and began flailing about trying to get the boom-stick out. Lennox grabbed the rope Sam's glove was attached to, but was unable to cut it. they managed to hit the release mere seconds before the boom-stick went off, which killed Starscream, but nearly fell to their deaths, only just saved by Bumblebee. Once they were sure Starscream was dead, Bumblebee went ahead to the edge of the river.
By the time the two human teams reached the bridge, a SEAL team arrived, informing Lennox of inbound TOMAHAWK missiles, and the military had accessed local security cameras. What they found was not encouraging: most of the Autobots had been taken captive by Decepticons lead by Soundwave. Realizing that the humans needed to get across the river, Dutch was able to hack the bridge controls and lower the bridge. Unfortunately, the orbiting pillars reached the necessary coordinates, and the ground based pillars began opening the space bridge. While this was going on, Wheelie and Brains managed to board a Decepticon cruiser and make their way to the control center. At the holding area, Dylan Gould was shocked that the Decepticons were taking prisoners, and encouraged them to kill the Autobots.
Soundwave happily concurred, declaring "no prisoners, only trophies". Ordering Que to his feet, the Autobot scientist was gunned down by Barricade while begging for mercy. Sam tried to activate a boom-stick, but it was damaged. Just as Soundwave was about to execute Bumblebee, Orbital Assault Carriers from the hijacked cruiser began crashing to the ground. The Autobots and Decepticons scrambled for cover, and Bumblebee was able to kill Soundwave in the ensuring confusion, then escape with the others. However, the cruiser carrying Wheelie and Brains crashed into the river.
Meeting up with some army troopers, Lennox and Epps's teams took positions for a strike on the Decepticons, who were investigating Soundwave's last stand. As Lennox's team parachuted in, Barricade was reprimanding the protoforms for allowing the Autobots to escape when snipers began firing at the Decepticons optics. Momentarily blinded, the several demolitions teams were able to attach explosives to the Decepticons feet, crippling Barricade and several protoforms enough for the humans to kill them. As the Decepticons returned fire, Lennox and his men parachuted onto Shockwave, with one trooper seriously damaging the large Decepticon, while Epps team opened fire on full auto, seriously disorienting Shockwave. With this, the Autobots arrived and attacked. Despite the promising opening, sheer firepower was on the Decepticons side, keeping the Autobots and NEST from reaching the pillars. Declaring that Earth was theirs, Sentinel Prime fully activated the space bridge, and Cybertron began appearing in orbit. Just then, Optimus Prime, freed from the cables, arrived and quite literally tore through every Decepticon standing between him and Sentinel. Finally reaching Shockwave, Optimus punched out half of his chest, then tore his eye out through his head. Firing Shockwave's cannon at the control pillar, Optimus brought down a small part of the building, interrupting the transport and leaving Cybertron in half.
Optimus then demanded that Sentinel confront him, and a furious Sentinel was only too willing to oblige. Using his Primax Blade to descend the building, Sentinel was dumbfounded that Optimus still sided with the humans, but Optimus countered that Sentinel was the one who taught him freedom was the right of all sentient beings. Drawing a sword and Energon-axe, Optimus engaged Sentinel, who vowed to reactivate the pillar, while Sam went off to try and reach it first. With the tide turning, the Autobots, NEST, and the military pushed forward. When Optimus started to get the upper hand over Sentinel, the elder Prime called in the Orbital Assault Carriers to attack Optimus. All the Orbital Assault Carriers. NEST was able to make contact with the remote guided TOMAHAWK missiles, which were five minutes out. With the Orbital Assault Carriers attacking Optimus, the Wreckers attacking the incoming ground Decepticons, and the rest of the Autobots engaging Sentinel, no Decepticons were left to reactivate the pillar, which fell to a cowering Dylan Gould. With the Orbital Assault Carriers on the verge of overwhelming Optimus, NEST was able to guide the missiles to the fighters, downing them.
As Sam made his way to the pillar, he encountered Gould, who tried to stop him at gunpoint. Sam tried to reason with the human agent, but Gould said there only one future for him. As some papers obstructed his vision, Sam attacked, but Gould was still able to reactivate the pillar. Megatron, allowing his Lensmeter Decepticons to repair him, rested easily as Carly approached the Lord High Protector. Carly then pointed out that while the Decepticons were conquering Earth, their leader would not be Megatron, but Sentinel Prime. Megatron was within a hair of killing her when he realized she was right. Meanwhile, Sentinel, under fire from more or less everything at this point, realized that he was losing and fled with Optimus hot on his heels. Optimus caught up with Sentinel at a bridge and the two fought once again. However, when Sentinel severed Optimus's right arm and knocked him to the ground, it came apparent that Optimus was not stronger then his mentor. Lamenting over how the Dynasty of Primes had been gods on Cybertron, Sentinel declared that on Earth, there could only be one.
Just as Sentinel was about to deliver the killing blow, an infuriated Megatron came in firing—at Sentinel, letting loose several thousand years of parental issues out. Sam quickly reappeared, and promptly killed Gould with the pillar itself. The Autobots overwhelmed the last Decepticon, and Ratchet and Bumblebee destroyed the pillar. The effects were instantaneous: not only were the remaining Decepticon ships pulled out of Chicago and into the collapsing space bridge, but the space bridge's collapse destroyed Cybertron in the process. Seeing the plan had failed, Megatron slyly proposed a truce with Optimus, his only stipulation remaining Decepticon leader. Megatron was confident Optimus would accept; they had fought for so long, Optimus declared that he would find out. Picking up his discarded axe, Optimus jammed the weapon into Megatron's head, then tore it off, killing Megatron. The badly wounded Sentinel pleaded for mercy, explaining that all he wanted was to save the Cybertronian race, which was why he betrayed his former pupil. Optimus claimed it was never about betraying Optimus; by allying with Megatron and planning to enslave humanity, Sentinel had betrayed himself. With bitter regret, Optimus Prime raised Megatron's fusion shotgun and executed Sentinel Prime.
With the battle over, Sam and Carly reunited, and with Cybertron lost, the Autobots accepted that Earth was now their home.
Transformers: Age of Extinction[]
When Cemetery Wind and Lockdown hunted down the Autobot, Ratchet, James Savoy told him that he lost a sister in the Battle of Chicago, before Lockdown killed Ratchet.
Later in the film we are shown that many things like the Battle of Chicago have been used to tarnish the image of the Autobots, not to mention the Transformers in general.