Playing around with this a bit, basically everything after the first Great War happens differently because it gets too implausible for me to buy into.
Seven-term President and
de facto dictator of America William Dudley Pelley, leader of the American Redemption Party and progenitor of Coming Race Theory. A clinically insane spiritualist who believed that Jesus spoke to him in dreams from a flying saucer crewed by reptilian aliens, Pelley dedicated his life to annihilating every trace of the Confederacy. Coming to power mostly by pure luck in the 1936 Presidential election, Pelley used a network of Redeemer Party-aligned National Protection Police to disappear dissidents who got too vocal and make sure the elections always came out in his favor, as well as keeping the former Confederacy under permanent martial law for decades and forcibly re-educating white Confederate youth in Yankee boarding schools. Fanatically opposed to the Confederate racial caste system, Pelley became enamored at an early age of Mexican hybrid-race theories, and promoted his belief that God had created the world for the sake of a new, "Coming Race" of mixed Yankees and blacks, a hybrid race with the strength of body and character unique to the noble Negro, and the entrepreneurial spirit and drive for adventure of the Yankee, all merged into one glorious creature with superior strength, constitution, intellect, faith, and moral fiber. Viewing the South as a "filthy country, full of a degenerate race of Norman brutes, incapable of high culture and inherently opposed to our Yankee race, who dare to oppress our valiant Negro brothers despite their own degeneracy", Pelley's United States crushed Jake Featherston's Confederacy in the Second Great War, forcibly annexing the region with the help of black rebels and massively superior industry, manpower, and armor, then set about restructuring society for the glory of the Coming Race. Black militias and Yankee occupation forces were reorganized into massive military police units who ruled the South with an iron fist, repossessing whatever they wished for formerly-oppressed blacks, and flooding the region with Yankee settlers and Yankee industry.
Pelley would die of a stroke in early 1965, shortly before he was to assume his eighth term in office as President. His successors would gradually reduce the pervasive police state, release political prisoners, and reduce government presence at elections (Pelley had still held elections, but even after the NPP stopped actively threatening people to make them vote Redeemer, the Redeemers tended to win 97% of the vote with 137% turnout in most elections, with only token delegations reserved for the Socialists and Loyal Democrats), finally limiting the President to two terms at the end of President King's administration in late 1972 (King wasn't running for re-election, believing that it was his place to make way for a candidate of the Coming Race, so it wasn't like it would cause a crisis or anything). The insane dictator remains a controversial figure in American politics, lionized as the hero who annihilated the Confederacy by nationalists, but also greatly disliked in many circles for his heavy-handed measures, dictatorial rule, and crimes against humanity.
President Martin Luther King, Jr., Pelley's successor. A pastor and an ardent believer in Coming Race Theory and the Redeemer cause, King, born in a sharecropper's hut in the Confederacy, was considered an unlikely successor to Pelley due to his quiet opposition within the Party to the rigging of elections and concerns about the suicide and abuse rate in Yankee re-education schools. However, when Party National Protection Police head Richard Nixon revealed his hated rival, Party propaganda chief John F. Kennedy, to be a serial sexual predator, and Party Speaker of the House Malcolm Little denounced both men, King won the primary (the only truly free election in America at the time) as a compromise candidate in a landslide. A well-spoken, handsome black man, King was popular with the people and a much sharper political actor than he let on, using Little's support to get Nixon and Kennedy kicked out of the Party and arrested, then doubling down on crushing the headless NPP and disseminating its more reliable personnel into actual government departments. Using the bully pulpit much like his predecessor, King was a more well-rounded speaker than the ranting, insane Pelley, and achieved considerable success.
During King's administration, the re-education program was ended, though at this point the damage had been done; the few Confederate diehards who'd escaped the Midwest labor camps were approaching retirement age, and an entire generation had grown up in Yankee re-education schools and was beginning to have kids of their own. Although some Redeemer occupation governments in the South weren't happy about letting the Dixies vote again, King being a black man himself definitely helped smooth things over.
Believing that the Coming Race's time was at hand (the first large cadre of interracial children now nearing 30), King approved a Constitutional amendment to establish Presidential term limits in 1972, then retired to a California villa with his family. He remained extremely popular throughout the USA and continued to speak publicly and hold sermons until his death in 2007.
House Minority Leader and later President Rosa Parks, certified after the Reunification as a member of the Coming Race due to her Native American, black, and Scots-Irish ancestry. Born into
de facto slavery (of the permanent debt slavery model) in the Confederacy, Parks rose to prominence when the Socialists won a significant minority in President King's first midterms, the first elections to take place without NPP guards ensuring that the ballot boxes were filled with enough straight-ticket Redeemer ballots. Winning re-election twice, Parks then ran for President, defeating Speaker Little and corrupt Senator Ronald Reagan, in what President King endorsed as "the triumph of the Coming Race and the beginning of the culmination of President Pelley's prophetic vision". Parks herself didn't believe any of that alien lizard Jesus claptrap, and instead proposed the elimination of formal racial divisions as part of the healing and de-Pelleyization process. This worked great on paper, not so well in practice, given the decades of Pelley's indoctrination and batshit crazy race propaganda in the South and the last gasp of white supremacist ideology in that region. Parks would serve two terms as President, before retiring to go work in Socialist Party-linked charities.
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Going to post the rest of this over the next 2 days, covering every President from Pelley to the modern day and the slow return of the USA to proper democracy.