Hearts of Iron II: Doomsday is stand-alone expansion of the Hearts of Iron II. The original game is included with improvements.
It is 1936 and Nazi Germany is about to change the course of world history. Years later, the Allies have defeated the Nazi threat and the choice to change history lies in the player's hands to alter the paths of the Allies or the Communists in what possibly may be World War III. Take the role of the government from one of 175 available countries to choose from, ranging from the year 1930 to 1953 as the largest countries in the world prepare for war: United States, China, Germany, France, United Kingdom, Soviet Union, and Japan.
There are four campaigns available (1936, 1939, 1941, and 1944) from the original game and one extra Doomsday scenario (1945) and three alternative What-If scenarios.
The game was set during the time period of 1939 to 1953. The reason for the year 1953 refers to historical death of Stalin (Soviet Union). The developers used this year to mark the "end" of the World War II conflict and possible "what-if's" since Stalin was one of the major key players in WW II.