|The following is based on Fallout Tactics and some details might contradict canon.|
Some time after the defeat of the Master in 2162, the Brotherhood of Steel constructed airships and dispatched some of its soldiers East, to track down and assess the extent of the remaining super mutant threat. However, a great storm broke the main airship and flung it far from its course. The other airships were torn apart and lost.
The mighty airship was badly damaged. The meteorological disturbances were so intense that sections of the craft were wrenched free of the ship and lost, leading to casualties among those onboard. Even the leaders of the expedition were not spared, with many of them being lost, including Paladin Latham. The survivors managed to keep their battered ship aloft, but eventually they came down on the ruined city's outskirts. Those who made it clear of the wreck eventually formed an organization called the Midwestern Brotherhood of Steel, which diverged greatly from the ideals of the original Brotherhood of Steel. In time, they established a harsh rule over the towns and villages near Chicago, controlled from Bunker Alpha. The sky over the city is always dark and stormy, and the city seems to be completely deserted.
In the decades following the war with Gammorin's Army and the war with the Calculator, the Midwestern Brotherhood slowly collapsed, and the entirety of the organization regrouped at Chicago. After the Destruction of Control Station ENCLAVE in 2242, an Enclave force that fled the oil rig landed in Chicago and set up outposts within the ruins. Nothing more is known about the Enclave's presence in Chicago, however, it can be assumed there is conflict between them and the Brotherhood.
- The remains of Chicago appear only in the Fallout Tactics intro but not in-game.
- Chicago is mentioned in conversations with Fallout 3 by Scribe Jameson or Scribe Rothchild about fighting super mutants or by asking about where the rest of the Brotherhood of Steel is.
- The city is also mentioned in Fallout: New Vegas on a recording found on ED-E during the quest ED-E My Love, hinting at an Enclave outpost located there.
- It is furthermore mentioned in the Fallout: New Vegas add-on Lonesome Road, when the copy of ED-E is telling the Courier about Whitley and his journey to Navarro, to which the Courier will reply, "What's a Chicago?"