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Originally created as a simple “who-would-you-vote-for” poll in the Shared Worlds forum by lord caedus, resulting in a huge - and only surprising in universe - victory for the Bernie Sanders-led Progressive Democrats over Hillary Clinton's Liberals, Mitt Romney's Conservatives, Ron Paul's Libertarians, Elizabeth May's Greens and Pat Buchanan's American Heritagers, the thread soon evolved into a universe of its own based on the poll and the posts in the poll thread, focused on a massive USA+Canada+Bahamas called the American Commonwealth and its politics, considerably more aligned with today's Canada than today's United States. A few contributors update the universe with political developments more or less based off the real world's events as well as information about the universe told through Wikipedia-style infoboxes or infodumps.
Admittedly, the world is a Type III on the Sliding Scale of Alternate History Plausibility, with very few fictional characters playing anything close to a major role over 250 years after the POD, as well as a somewhat diminished Butterfly Effect causing TTL's history to run similar to OTL history.
A second general election was held in November 2013 and resulted in a virtual three-way tie between the Progressive Democrats, Liberals and Conservatives, although this poll was “skewed” to provide a plausible outcome given the trends previously established in the thread by the contributors. The Liberals and Progressive Democrats formed a coalition government with the Liberals as senior partner, and the inevitable predictions for a third election in 2014 were quashed by lord caedus because he did not want to do so much election work again so soon.
The main POD is an avoidance of the American Revolution as a result of successful negotiations in the middle of the crises following the Seven Year's War. The resulting negotiations led to a Canada-esque Commonwealth of America (commonly renamed the “American Commonwealth” both in-universe and out). Benjamin Franklin, as the main proponent of such a scheme (see his earlier Albany Plan), becomes the “Father of the Commonwealth” and the first American Prime Minister.
The Commonwealth plays a subservient role to Great Britain for the next fifty years, with many Americans participating in the Napoleonic Wars in Europe or forcing Napoleon out of Louisiana in 1803 (there was no Louisiana Purchase ITTL). The abolition of slavery across the empire in 1832 during the ministry of John Calhoun causes a prolonged version of the Nullification Crisis (called the “Emancipation Nullification Crisis”) that eventually sees slavery abolished after Calhoun is defeated by Henry Clay in the 1839 elections. The annexation of the Republic of Texas causes TTL's Mexican War, the noticeable difference being that the United Kingdom props up the struggling Republic of Yucatan during the conflict, causing that republic's survival to the present day.
As a result of a successful Mexican War, British soldiers leave the commonwealth after realizing that the colonials have got it under control. Unfortunately, less than three years after the Mexican War ends, the Republican Uprising breaks out in 1851. The uprising fails because of the fragmented nature of the rebels, and it fails within a year, with Atlanta being burned during the final days of the revolt (a shoutout to Sherman's March to the Sea). Thus, there is no Civil War, but Americans participate in several wars that they did not IOTL between 1861 and 1914: the French-Mexican War (which wound up being ended before Maximilian could become emperor due to the fact that the Commonwealth did not have a breakaway south to deal with), the Colombian Intervention (a joint American/British filibuster that ended the Colombian civil war in 1862, but not before a certain Captain Custer rushed foolishly into Bogota and got his regiment destroyed), and the Second Boer War. TTL's Spanish-American War is the Cuban War, which sees Great Britain help America rip some of Spain's remaining colonies away and results in America gaining Puerto Rico while Great Britain nabs Guam and the Philippines.
In 1914, the Americans are led by Eugene Debs, the first socialist prime minister in the world and in return for his country entering World War I, he makes the British promise independence (by way of an earlier Statue of Westminster) after the war's conclusion. The war goes similar to OTL, with the only major changes being American-British policing of the Dardanelles causing Greece to retain almost all of the western side of the Bosphorus Strait. The Great Depression hits around the same time, but with different causes. The fall of the Social Democrats as a result of World War I and the Roaring Twenties sets up the miraculous turnaround for Bernie Sanders's Progressive Democrats in 90 years' time (when the TL “started”).
William Mackenzie King leads the Commonwealth through the Great Depression and World War II. Due to political pressures, Mackenzie King is forced to keep Commonwealth involvement in Europe at a bare minimum until the attacks on Pearl Harbor cause the Commonwealth to engage in total war against Nazi Germany and Imperial Japan. Mackenzie King also reluctantly drops the atomic bombs on Hiroshima and Nagasaki in 1945 as a result of pressure from one Harry S. Truman.
The Commonwealth emerges as the dominant rival to the Soviet Union after the war, and the Cold War proceeds largely along similar lines as OTL. The major differences include:
Following the Cold War, TTL's America largely follows in the path of the OTL United States with regards to foreign adventures, with the main exception being engagement in the Balkans in 1998 under Dick Gephardt that sees Kosovo become independent much earlier. With regards to domestic politics, the country runs through seven prime ministers (G.W. Bush, Paul Tsongas, Joe Clark, Gephardt, George W. Bush, John McCain & Hillary Clinton) before Bernie Sanders is elected in 2010, and then Jeanne Shaheen in 2013.
As mentioned, the TL is very convergent with OTL, so it's much easier to mention what's not similar to OTL during the present*:
*-Note: Many OTL nations have different national leaders ITTL.
The party system is somewhat influx in-universe, as the Progressive Democrats, a left-wing party similar to Canada's NDP and the progressive members of the Democratic Party, emerged as a major party in 2010. They are currently led by Amy Klobuchar, who narrowly defeated Thomas Mulcair to take over from Bernie Sanders in May 2014.
The largest major party (seats-wise) are the Liberals, led by Jeanne Shaheen (who defeated Barack Obama and Tim Kaine for the party leadership in early 2011) and make up mostly members of the OTL Democratic Party and Liberal Party of Canada. They currently are the slightly senior partners in a coalition with the Progressive Democrats.
Rounding out the major parties are the Conservatives who are split between the Rockefeller Republican-esque “Red Tories” and the more conservative (in this case meaning Reagan-era Republicans without an emphasis on social issues) “Blue Tories”. The Conservatives are led by Bobby Jindal, who has revitalized the Blue Tory wing in his party and dismantled the former Progressive Democratic-Conservative coalition that ruled from 2010 until early 2013.
“Second-tier” parties, (parties that do not have the support to make their leader prime minister but can be kingmakers in coalition politics) include: the Libertarians, led by Bob Barr (who took over for a retiring Ron Paul), the environmentalist Greens (led by Elizabeth May and who supported the minority Progressive Democratic government from early 2013 until the general election later that year), and the right-wing American Heritage Party (led by Tom Tancredo), which is made up of a combination of nativists, the religious right and hardcore social conservatives
The only other parties in the current federal parliament include: the Progressive Conservatives (led by John Tory), the remnant of a group of Conservatives who split off when Reagan became their party leader, now mostly relegated to New England. Alaskan Independence (led by Don Young) are a right-wing party exclusive to Alaska who generally take that province's riding seat. The Republican Party, led by Russ Feingold, is a left-wing party that posits the unpopular (IU) idea of abolishing the monarchy.
Like Canada, the party system is different for each province compared to the national one (although Ungava, Nunavut and the Northwest Territories use consensus government instead of a party-based system). Many provinces' politics somewhat mirror the federal scene, but many provinces have their own unique parties or their own dynamics which are very odd by federal standards, with the most unique being Columbia and Rhode Island.