XCOM: Long War is a fan-made partial conversion mod for XCOM: Enemy Unknown and its expansion, XCOM: Enemy Within. Almost every aspect of the original game is altered, creating a longer, more complex campaign that presents players with more strategic choices and customization options. Long War adds a significant number of new soldier classes, abilities, weapons, armors, and usable items, and also introduces new features, including soldier fatigue and improvements to alien units over the course of the game.