I'm wondering if a great evil like the Holocaust was able to materialize because it happened by dribs and drabs. I read somewhere that a woman who had been freed from a camp applied for asylum as a 'political prisoner' because no one really had a full grasp of what had happened, or called it the Holocaust, until years later. This made me wonder whether those who carried it out also didn't really have a grasp on what was happening or how it would end. If Hitler had just carried out his military campaigns and there had been no death camps, would that have changed the course of the war?
First, concentration camps and death camps are two separate things. A concentration camp was analogous to a prison camp of some sort. Lots of people imprisoned, often for forced labor. Part of the confusion stems from the fact that a lot of people were killed there, because there were policies in place to that end (i.e. starvation). Death camps were just death factories--few people were imprisoned there, and it was built with the sole intent of murdering people in more efficient methods than had previously been used (mass shootings).
Anyway, you're basically asking one of the big questions in study of the Holocaust. Scholars disagree at what point the decision was made to commit genocide. Certainly during ghettoization (where conditions were intentionally made unliveable) and when the mobile killing squads started massacring people the decision was made--there were changes to how, but it was already in progress.