The War in The book of Eli was an event that occurred 30 years prior to the current day events in the movie. A poster when Eli is in the hotel room and Sacara's mother walks in to give him treats says or shows 2024 supposing that the War happened in the year 2024 also making the present events be in 2054/2055. Eli also states that the war might have happened because of these books. The book is the bible, and the one he possesses is the last one left)

Eli states that after the war it tore a hole in the sky that burnt everything