A union of Southwestern states that, in this timeline, seceded after the stock market crashed in 1929. (I'm starting to draw up a backstory now; more information on Jefferson and the other nations should pop up soon.)
And here's part of my draft. It covers what lead to Jeffeson's formation, and will eventually include the map's other nations.
1915: Woodrow Wilson joins the Allied Powers in WW1 at the urging of war-hungry members of his cabinet after the sinking of the Lusitania. He sends troops to help his new European allies. Many of the new arrivals are unprepared for the new kind of war that is being fought in Europe, and are soon sent to Ypres, where they are killed en masse. On the home front, views on the war are highly polarized, particularly in cities with large immigrant populations. Riots flare up periodically, and strikes are common.
As WW1 thunders on, Wilson passes the Sedition and Espionage Acts, and creates several committees to manage resources for the war. Although most states accept this, these actions energize several radicals across the country, giving rise to Regionalist movements in the South.
1916: The slaughter in Europe and back-and-forth nature of the war, and arrests/imprisonments due to the Espionage and Sedition Acts begin to slowly polarize the nation. Regionalists gain influence in the South, while Socialists establish themselves in Northern cities, particularly in Michigan.
1917: The tide of war begins to turn towards the Allies with victories against the Ottomans and in Europe, but the collapse of Russia worries many, and convinces many moderates to oppose the war. Regionalists capitalize on the discovery of the “Zimmerman Note” and gain great influence in the Southwest, while Socialist movements in Michigan gain members from disaffected factory workers. Dedicated Regionalists are emerging in influential positions in parts of the South and much of the Southwest.
1918: WW1 ends with Allied victory, but dissent simmers, especially in the Southwest and Michigan. Socialist movement begins to spread to "steel belt”, while Regionalist movements form in Canada.
1919-1928: The enactment of Prohibition is controversial and raises dissent in “wet” states, but the prosperity of the “Roaring Twenties" severely saps strength from Socialists and Southern Regionalists, but Southwestern movement remains strong, with leading members of the movement in government positions.
1929: Stock market collapses, inducing nation-wide panic. By this time drenched with Regionalist dogma, Texas secedes, soon followed by many Southwestern states. They eventually unite as Jefferson, associating their states’-rights politics with the famed Revolutionary War hero.