Alright, this one's a bit far-fetched. In fact, its pretty much impossible, but I don't think you'll get much else that isn't:
People to this day are still debating the reason for the Second American Civil War and the collapse of the United States. Following the Allied victory in the First Great War the United States enjoyed itself in a state of leisure and excess during the Roaring 20’s. The good times simply were not to last with the start of the Great Depression, Black Friday; the several block long soup lines and the Dust Bowl.
The event that was the sign of worse things to come was Hoover’s handling of the Bonus Army. After an incident involving Bonus Army members shooting and killing a soldier and two cops Hoover sent the army to break the Bonus Army encampment. The two sides involved in a gun fight with several dead and the camp destroyed by superior army forces. Two days later President Hoover was shot by a assassin starting riots and strikes across the nation and Vice-President declaring marshal law shortly in hopes of bringing order.
America placed its hopes later that year upon New York Governor Franklin Delano Roosevelt. FDR destroyed Curtis in the polls with Curtis only holding Maine and FDR winning in the single greatest electoral and popular landslide of American history. That too was simply not to be as on February 15th the President-Elect was assassinated by Giuseppe Zangara. The events that occurred after the assassination started the Second American Civil War. With death of John Garner of a heart attack the US government is gone replaced by several factions fighting for control of the former United States and to remake the republic of or perhaps one more in their image…
Jump to 1936, the civil war is raging in earnest across the country with foreigners begin backing sides. Mexico and Canada are both suspected of secretly slipping arms and support to friendly forces over the border. Britain and France have pledged not to take any part and are refusing to sell weapons, however volunteers are still trickling in to support their ideology. The big players though are the Soviet Union and Nazi Germany, both of which are funneling large quantities of weapons as well as advisors and even tanks/aircraft to far-left and far-right factions. In July of that year, Germany sends a small army of volunteers, known as the "Condor Legion" to the United States, which would grow in size over the years as they advanced Fascist and white supremacy interests in the war.
In 1940, war has broken out in Europe. Despite their conflict in North America, Stalin decides to stay neutral and play the Germans against the allies by providing them with the raw materials they need in exchange for a non-aggression pact. Britain uses her navy to cut off the Germans in America, but the Nazis and their "friends" manage to hold on nevertheless. After Germany's stunning victory in France and Japan's invasion of their colonies, Britain signs a peace deal late in the year which frees France but places harsh conditions against them and cedes territory to Germany (though Britain is left untouched).
With the war at home won, Hitler becomes obsessed with realizing a Fascist German-dominated United States. Against the advice of his generals, he orders massive increases in intervention forces in the USA, with entire armored divisions being shifted over by the end of 1941. Britain is angered and threatens to blockade them on several occasions, but doesn't take action due the fear that Germany will invade France again and the fact that Japan is proving to be much more more difficult to defeat than they expected. Meanwhile Stalin, so greatly alarmed by the speed with which the Germans overran France and troubled by the dismal performance of Soviet Union's armies in Finland, begins halting support for the leftists in the United States in order to appease the Nazis.
By 1943, nearly the entirety of the United States has been conquered, and the Germans put a puppet Fascist regime in power while keeping soldiers in the country to enforce their will and combat the powerful resistance movements throughout the country. Dissidents are used as slave labor, as the nation is exploited for oil, grain and raw materials by the Germans. The Final Solution are brought over to the United States, and expanded to include African Americans. Millions would die in Hitler's quest to "purify" the racially tainted USA, and transform it into Germany's perfect Aryan ally. Meanwhile, with the help of the Soviet Union, Japanese forces in Asia are defeated and their navy loses control of the oil sources.
In 1946, the United States is finally liberated, when an combined alliance of Britain, France and the Soviet Union defeat Germany. Though reconstruction efforts take initially take place, these are quickly drained of funding as a Cold War develops between Britain and the Soviet Union when Stalin puts Communist Party of China in control after moping up the Japanese. Nuclear weapons are developed during this period, preventing all-out war due to their destructiveness.
The United States becomes an impoverished and backwards nation wracked by violent coups and political disunity. Britain struggles to hold together her empire and those of her allies as Soviet backed independence movements rebel against their colonists. They eventually "lose" the cold war during the 1980s when military over-spending causes their economies to crash and capitalist governments begin collapsing in Europe.
Skip ahead to the present, 2013. The United States was slow to adopt socialist reforms, but has managed to do so, though keeping a less authoritarian government. But over the last few decades, the nation has seen rapid development of its economy as it takes advantage of its cheap labor and abundant natural resources. The USA is seen as a prospective rival superpower to the Soviet Union in the future.
They do provide some support to their "allies" the Canadians, who have become a stagnant impoverished country clinging to capitalist ways; but not too much, since even the USA acknowledges that their government is a bit crazy.
