This means that any mistakes are irreversible. Single player also has the option of "Ironman" mode, which locks several settings such as difficulty, and removes the control of saving the game from the player. Players can choose to play single player mode versus the AI, or multiplayer over a LAN or the Internet against a mix of human and AI opponents. Some of these random events are driven by an individual country's history, while some can apply to any country and serve generally to enhance the "flavor" of the game. These events can be either helpful or harmful. Gameplay is influenced by random events that arise every so often for the player. Military technology unlocks advancements such as new types of land units, improved unit morale, combat tactics, and new buildings.
Diplomatic technology unlocks advancements such as naval units, improvements in trade, new buildings, and improved colonial expansion.