Aggression: Reign over Europe uses an unusual scenario for strategy games: it covers both World Wars and is set between 1910 and 1950. The player takes the role of either Germany, Britain, Russia or France during the four campaigns. Most of the time is spent on the European map where the player takes care of the military and economic development of his nations, e.g. with diplomacy or trading. This part is played in real-time but can be paused at any time.
Since the goal is gain reign over Europe there are also a lot of battles to be fought. The player can either let them calculate them or participate in them in real-time tactics battles. Like in similar games the players manages big armies and can use several tactics, e.g. flanking the enemy. Important to note is that there are about 150 different units but no naval ones. There are also six scenarios with single battles.