I gave a talk at PDXCon 2021 about this, if you'd like the history in that form. You can find the recording here.
When Crusader Kings was released, it included an exporter to Europa Universalis 2. This inspired a multiplayer group to try a campaign from CK to EU2. Rolf Andreassen (King of Men) was unsatisfied with the quality and wrote a fan-made converter. Around the same time, Chaingun created an EU2 to Vic converter, which later saw signficant improvements from montyP.
When the multiplayer group began their campaign, they also wrote After Action Reports (AARs) for it, creating the first megacampaign AAR. Portions of is can be read on King of Men's webpage or on the Paradox forums.
When Victoria was given the expansion Revolutions, it contined an exporter to HoI2, allowing an automated campaign across the four major works in Paradox's portfolio. As sequels were released to the different games, different fans created converters to match. This has continued to the modern day, with most converters now done by a coordinated team.
An early version of EU3 to Vic2 inspired a humorous review, leading to the idea of Secret Denmark. The converters team quickly added it as an easter egg. later Paradox would do the same.
Over the years, many AARs and LPs have been released in many places: Something Awful, the Paradox Forums, Youtube, Reddit, and more. Known works are recorded below.
Aug 27, 2010 - FlyingMacguffin’s Brittany megacampaign begins
July 9, 2012 - Kailvin’s Rise of the Palmyrene Empire megacampaign begins
Jan 22, 2017 - WonderProductions’ first megacampaign
Feb 25, 2017 - WonderProductions provides converter tutorial video
Sep 8, 2018 - Drew Durnil’s observer megacampaign
Dec 20, 2018 - iSorrowproductions starts doing megacampaigns each December
Oct 8, 2007 - “Kingdom Come” begins (Fintilgin)
Nov 25, 2007 - “The Eyes of Texas Are Upon You” begins (Danimo)
Mar 2, 2008 - “Hohenzollern” begins (Wiz)
Nov 28, 2009 - “ I've lost track of all these Romes” (Srbja and Friends) begins (Sam.)
Aug 4, 2011 - “Islam is the Light: Azerbaijan Paradox Mega-LP” begins (Wiz)
Mar 17, 2013 - “Flamboyant Schemers” begins (Thanqol)
Oct 5, 2013 - “One Thousand Years of Misrule” begins (Grey Hunter)
Jan 18, 2014 - “Blood in the Bosphorus” begins (Empress Theonora)
Jan 5, 2015 - The Graveyard of Empires: An Afghan Paradox Mega-LP (Mr.Morgenstern)
Apr 25, 2015 - “Let’s Wear Black” begins (Ofaloaf)
Jan 3, 2017 - “Al Andalus” begins (Hashim)
Sep 20, 2017 - “For The Love Of God - Papal Paradox Megacampaign” begins (Crisis Now)
May 29, 2019 - “Roof of the World” begins (Kangxi)
May 1, 2005 - “The Great Game” begins (Ynglings)
Dec 12, 2007 - “There Will Be War” begins (second Yngling timeline)
May 11, 2010: “Children of the Fatherland” begins (KoMnenoi)
Jan 28, 2013: “God Will Know His Own” begins (MacRaghnalls)
Nov 15, 2014: “Recessional” begins (de Errolan; ended in CK)
Aug 15, 2015: “Azure Three Bezants” begins (Aiello)
May 27, 2017 - “Song of the Dead” begins (Ynglings, ended in EU)
Oct 15, 2017 - “Song of the Dead II” begins (Ynglings)
Jan 4, 2019 - “No Crowns for Good Kings” begins (van Roland, ended in CK)
Mar 31, 2019 - “Invictus” begins (Ynglings)
Mar 11, 2020 - “The Widow’s Party” begins (KoMnenoi)
Apr 25, 2021 - “Knights Last Gleaming” first session
Sep 14, 2012 - “The rise of the Hohenzollerns” begins (Avindian)
Oct 25, 2012 - “Return of the Romans” begins (Idhrendur, ends in failure)
Nov 3, 2012 - “The Empire Strikes Back” begins (Idhrendur)
Oct 30, 2015 - “The Hohenzollern Empire” begins (zenphoenix)
Secret Denmark is based on a EU4 to Vic2 conversion, but from early in the converter, when it still had a lot of EU3 to Vic2 code. The post (by Patter Song) was laughing at the resulting jank.
EU3 to Vic2 made a save, so relied on existing Vic2 tags. It was clever, tried to directly assign (Spain to Spain), regionally assign (Castille might convert to Portugal), use general leftover, and finally dip into the dynamic Vic2 tags. Many countries would be correct, but others would be very strange. Lots of “Mighty ”, “Strong ”, “The Federation ”, “Secret ”, etc. The converter broke those to drop the region part, of course.
Vic2 with expansions was an early experiment in clever names printed on the map. Over your own territory, it would print your own name. Over other territory it would try to be more descriptive (useful in an age of colonialism). How did it tell the difference? Cores! In land with your own cores, it just puts your name. In areas without your cores, but someone else’s it prints , giving names like British Canada.
Putting those together, the converter gave a bunch of cores to Denmark, which was a dead country, including tags in Greenland. The actual country controlling Greenland (and parts of Canada) was Secret. So then Greenland gets marked as ‘Secret Denmark’. Sadly the original post doesn’t directly screenshot this.
December 11, 2001 - EU2 released
November 24, 2002 - HoI released
Nov 2003 - Vic released
Apr 23, 2004 - CK released (has converter to EU2)
Jun 16, 2004 - EU2 to Vic released (Chaingun, later significant updates by montyP)
Ca 2005 - CK1 to EU2 released (KoM)
4 January 2005 - HoI2 released
May 1, 2005 - “The Great Game” begins (Ynglings)
Aug 17, 2006 - Vic:Rev released (contains exporter to HoI2)
Jan 2007 - EU3 released
Feb 10, 2007 - EU3 to Vic:Rev released (MontyP, then passed between many people)
Aug 2007 - EU3 NA released
Sep 18, 2007 - CK to EU3 converter released (yvesp)
Oct 2007 - CKDV released
Oct 8, 2007 - Kingdom Come LP begins (Fintilgin)
Nov 25, 2007 - “The Eyes of Texas Are Upon You” begins (Danimo)
Dec 12, 2007 - “There Will Be War” begins (second Yngling timeline)
Mar 2, 2008 - Hohenzollern LP begins (Wiz)
Mar 19, 2008 - CK to EU3 save converter released (ulmont)
May 2008 - EU3 IN released
Sep 2009 - HoI3 released
Dec 2009 - EU3 HttT released
Jan 16, 2010 - CKDV to EU3:HttT released (Idhrendur’s first converter)
May 11, 2010: “Children of the Fatherland” begins (KoMnenoi)
Jun 2010 - HoI3 SF released
Aug 10, 2010 - EU3 to Vic2 and Vic2 to HoI3 announced (SidMeier, Idhrendur eventually takes over)
Aug 13, 2010 - Vic2 released
Aug 27, 2010 - FlyingMacguffin’s Brittany megacampaign begins (one of the first, if not the first youtube megacampaigns)
Dec 2010 - EU3 DW released
Jun 2011 - HoI3 FtM released
Jun 30, 2011 - CKDV to EU3:DW released (KoM)
Feb 2, 2012 - Vic2 AHD released
Feb 4, 2012 - Vic2 to HoI3 splits to own thread (Idhrendur/DasGuntLord)
Feb 14, 2012 - CK2 released
Feb 18, 2012 - CK2 to EU3 announced (Idhrendur)
Mar 25, 2012 - Vic2 to AoD released (KoM)
May 25, 2012 - CK2 to EU3 - C# / Lua announced
Jun 10, 2012 - EU3:DW to Vic2:AHD released (KoM)
Sep 2012 - HoI3 TFH released
Sep 14, 2012 - “The rise of the Hohenzollerns” begins (Avindian)
Oct 25, 2012 - “Return of the Romans” begins (Idhrendur, ends in failure)
Nov 3, 2012 - “The Empire Strikes Back” begins (Idhrendur)
Jan 28, 2013: “God Will Know His Own” begins (MacRaghnalls)
Mar 30, 2013 - CK2 to EU3 released (KoM)
Apr 16, 2013 - Vic2 HoD released
Aug 10, 2013 - EU4 to Vic2 announced (and switch to making mods instead of saves)
Aug 13, 2013 - EU4 release (CK2 exporter created)
Jan 18, 2014 - “Blood in the Bosphorus” begins (Empress Theonora)
Feb 16, 2014 - V2 to HoI3 released (KoM)
May 8, 2014 - Secret Denmark becomes known
Nov 15, 2014: “Recessional” begins (de Errolan; ended in CK)
Apr 10, 2015 - Vic2 to DH announced
Apr 25, 2015 - Let’s Wear Black begins (Ofaloaf)
Aug 6, 2015 - CK2 to EU4 released (KoM)
Aug 15, 2015: “Azure Three Bezants” begins (Aiello)
Oct 30, 2015 - “The Hohenzollern Empire” begins (zenphoenix)
Mar 23, 2016 - Vic2 to HoI4 announced
Jun 6, 2016 - HoI4 released
Jan 3, 2017 - “Al Andalus” begins (Hashim)
Jan 22, 2017 - WonderProductions’ first megacampaign (youtube)
Feb 25, 2017 - WonderProductions provides converter tutorial video (only one known)
May 27, 2017 - “Song of the Dead” begins (Ynglings, ended in EU)
July 11, 2017 - Last update of “The Empire Strikes Back”
Oct 15, 2017 - “Song of the Dead II” begins (Ynglings)
Sep 8, 2018 - Drew Durnil’s observer megacampaign (immensely popular, 2.6M views, really popularized the idea)
Dec 20, 2018 - iSorrowproductions starts doing megacampaigns each December (we see notable upticks in subscriber count each time)
Jan 4, 2019 - “No Crowns for Good Kings” begins (van Roland, ended in CK)
Mar 31, 2019 - “Invictus” begins (Ynglings)
Mar 11, 2020 - “The Widow’s Party” begins (KoMnenoi)
Apr 14, 2020 - CK2 to EU4 announced (replacing DLC converter)
May 29, 2019 - “Roof of the World” begins (Kangxi)
Sept 1, 2020 - CK3 released, Imperator to CK3 announced, CK3 to EU4 announced
Sept 27, 2020 - CK3 to EU4 released
Oct 11, 2020 - Imperator to CK3 released
Apr 25, 2021 - “Knights Last Gleaming” first session
Nov 5, 2021 - Imperator to CK2 released
May 21, 2022 - Victoria 3 announced - EU4 to Vic3 and Vic3 to HoI4 announced.
Oct 25, 2022 - Victoria 3 released
Jan 21, 2023 - EU4 to Vic3 released