Iguru senso is a Genjutsu used by the Uchiha of the 9th Dimension. The only shinobi who can use the Genjutsu wield the Etenral Mangekyo, or Post-Mangekyo, which develops upon destroying a whole civilization.
Iguru Senso puts the target in a War, the genjutsu's strength depends on the user, if a Ninja is strong enough the Genjutsu can make the targer think the War has been going on since their birth. 88% of the time they do not realize they are in a Genjutsu. In Iguru Senso strong ninja like Itachi Uchiha or Madara Uchiha will attack you, or other Ninja from the 9th Dimension. In some cases the Genjutsu makes you fight and kill comrades, family, and friends. If you die in the Genjutsu, you die out of it as well.