Some of you may already be aware of the history of HOI2 and its many variants but for those who aren't this is for you.
Hearts of Iron 2 was released on January 2005
Hearts of Iron II was commercially successful for Paradox; Hanza Aziz of Destructoid called it the company's "first major hit". In the United States alone, it sold 80,000 copies on a marketing budget of $75,000.
On Metacritic the following reception was achieved by Paradox Development Studio:
Heart of Iron II: 83/100 from the professional critics and 8.6/10 from the users.
Doomsday: 80/100 from the professional critics and 8.8/10 from the users.
Hearts of Iron II was a finalist for PC Gamer US's "Best Real-Time Strategy Game 2005" award, which ultimately went to Age of Empires III. It was also nominated for the 2004 Charles S. Roberts Award for "Best 20th Century Era Computer Wargame", but lost to Battles in Normandy.
Doomsday (stand-alone) was released on April 2006
In November 2005, a stand-alone expansion pack to the game, Hearts of Iron II: Doomsday, was released on April 4, 2006. It contains everything that was in the original game while highlighting and expanding the period after historical World War II, including a hypothetical nuclear war between the Soviet Union and the Allies. The expansion pack features among other things a reworked intelligence model (which allows the player to use espionage, sabotage and other things in an "intelligence page" accessible through the main screen), improved AI and a scenario editor.
Doomsday also features some other changes and additions such as:
Additional graphics such as bomber sprites
Hospitals that recover manpower losses
A "do not upgrade" button for divisions
The option of automating the production sliders
Submarines have separate stats for convoy raiding and naval combat
An extended timeframe — the game end date has been changed to 1953
New technologies to bring the game into the cold war era
An included scenario editor
The ability to trade divisions between nations
The ability to attach escorts while recruiting divisions
Armageddon (booster pack) was released on April 2007
Another expansion was released in April 2007 in an alternate history scenario called Hearts of Iron II: Armageddon. It further allows more time and the player has the ability to choose 1964 as the end point. It allows the adding of modules to ships (such as improved radar, fire-control, anti-submarine or anti-aircraft weaponry) and submits two new scenarios for play, as well as an enhanced AI.
Armageddon also features some other changes and additions such as:
Player can allow or disallow democracies to declare war on the main menu options screen
Player may choose when the time of play will end, ranging as early as 1940 to as late as 1964
Player may choose to get the full industrial capacity of an annexed country, or not
Player may choose to use tech teams of an annexed country or not
New brigade attachments for ships
Diplomatic option to refuse expeditionary forces from player's allies
Anthology was released on 31st August 2007
This was the last release of a Paradox developed Hearts of Iron II game.
Complete set consisting of four products. These are primarily the first two parts of the "Hearts of Iron" (ie. HOI1 and HOI2) series. In addition, included were stand-alone add-on "Doomsday" and booster pack "Armageddon".
This was the last HOI2 release that was developed by Paradox. The following 3 were by different developers and Paradox was the publisher only.
Arsenal of Democracy (stand-alone) was released on 23rd February 2010
Developed by BL-Logic, a development studio made up by fans of the Hearts of Iron series and active member of the modding community, Arsenal of Democracy is the ultimate World War II simulation and is described by Project Leader Lennart Berg as “Hearts of Iron II on steroids!
Increased resolution and windowed mode freely selectable
Totally reworked combat mechanics, new missions and realistic combat behavior and losses
Several new technologies
New espionage interface and reworked espionage system
One of the most detailed economy and production system found in any Hearts of Iron game
Realistic logistics system
Everything is moddable
AI reworked and now poses a genuine threat, even to experienced players
4 new battle scenarios
Iron Cross (expansion pack) was released on 10th July 2010
Contrary to the core game, Iron Cross was developed by Irshappa. The player assumes control of a country of their choice and leads their people to victory in the Second World War.
According to the creator, one of the largest novelties introduced in the expansion is a completely re-built map enriched with over 4000 new provinces. Also, the historical period encompassed by the game was lengthened – Iron Cross presents historical events that took place in the years 1933-1964. As a result, the game was extended with over 6000 new events.
The player also has new units and brigades at their disposal, among which one can find special forces, infantry regiments or heavy artillery. Moreover, the technology tree was also modified – a new, realistic development system was implemented here along with over 800 technologies to choose from. Gameplay as such became deeper, because of the improvements introduced into the in-game AI. On top of that, the creator added missions from the base game to Iron Cross – importantly, the new features function in case of those as well.
Darkest Hour (stand-alone) was released on 5th April 2011
Developed by a team of experienced modders (Martin Ivanov is the name in Steam but others were also involved) from the Paradox forum, Darkest Hour is a stand-alone Hearts of Iron game featuring a mixture of short and in-depth campaigns set across the darkest chapters of the 20th century, from the outbreak of the Great War up to the onset of the Cold War. Darkest Hour will introduce a new artificial intelligence that is now able to react to hundreds of different situations simultaneously, along with a dynamic diplomatic system that will allow the player to have a real impact on the course of history.
Short and grand campaigns allow players to experience the darkest hours of the 20th century, from the Great War to the onset of the Cold War
New map, redesigned to offer greater detail as well as strategic and tactical opportunities
Dynamic diplomatic system giving the player greater influence on the course of events
New artificial intelligence capable of reacting to hundreds of different situations
New decisions system