In 2031, a major earthquake sunk most of Southern California into the ocean. With the United States government focusing on the disaster on the ex-West Coast, the needs of the other parts of the country went unmet. In 2031, Utah announced its intention to secede from the United States, declaring its independence and annexing what was left of Arizona and Nevada. Inspired by Utah's example, fringe groups in Texas declared independence as well.
Also inspired by them were the Northwest Secessionist Forces, made up of various paramilitary groups in Wyoming, Montana, Idaho, Washington, and Oregon, who banded together with Utah and Texas. In response, the US government intervened.
While the details of the conflict are unknown, these efforts at secession all failed and the would-be secessionists were pushed back to the margins of society. However, martial law still exists in some portions of these states.
One of the legacies of the Northwest War are FBI-run "good behavior" camps.
Despite the country being back together, the NSF continues to be a problem. Comments by JC hint that the US might be on the verge of a third civil war.