Hearts of Iron

Hearts of Iron (HOI) is a grand strategy real-time simulation game developed by Paradox Interactive in Sweden. 
Series.
Four series have been published:
In this game, the player has all military authority over their selected nation. World War II is the background of this game. So the player can select all nations that existed when WW2 occurred. The player’s goal is surviving in the historical flood of WW2 and conquering the world. In order to survive in the game, the player has to develop his/her nation’s technology level and organize the nation’s economy for war. And, because each political regime has different characteristics in the process of war, a political statement can be important too. However, because this game is a war game, the most important thing is making the army, navy, and air force, and controlling them to make your nation larger.