When Did the Holocaust Happen?

I remember reading Dwight Eisenhower's "Crusade in Europe" (now a politically incorrect title) after it came out in 1948.  He describes his reaction to the death camps, including pictures of the survivors.  Then in the 1950's there was the "Diary of Anne Frank". 

But the "holocaust" didn't really occur, it didn't take shape as a narrative with a name and an accepted history until later, as shown in this Google ngram.